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PRACTICAL  SANITARY  SCIENCE 


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PRACTICAL 

SANITARY    SCIENCE 

A  HANDBOOK  FOR  THE  PUBLIC 
HEALTH  LABORATORY 


BY 

DAVID   SOMMERVILLE 

B.A.,  M.Sc,  M.D.,  M.R.C.P.  (Lond.),  D.P.H.  (Camb.),  F.C.S. 

ASSISTANT-PROFESSOR    OF    HYGIENE   AND    PUBLIC    HEALTH,    WITH    CHARGE  OF  THE  LABORATORIES 

OF   HYGIENIC   CHEMISTRY   AND   PHYSICS,   UNIVERSITY   OF  LONDON   KINg's    COLLEGE;   EXAMINER 

IN  BACTERIOLOGY   AND   CHEMISTRY,    B.SC.    (pUBLIC    HEALTH),    UNIVERSITY   OF   GLASGOW  J 

EXAMINER    IN    D.P.H.,    UNIVERSITY    OF  ABERDEEN;    MEDICAL   OFFICER   OF    HEALTH, 

harrow;  late  DEMONSTRATOR  OF  PHYSIOLOGY  IN  THE  MEDICAL  SCHOOL 

OF  ST.  Thomas's  hospital 


SECOND  EDITION 


NEW    YORK 
WILLIAM    WOOD    &    COMPANY 

MDCCCCXV 


\  r^  f 


>"^ 


K  A  4  X6' 


PREFACE 

TO 

THE  SECOND  EDITION 

The  arrangement  in  chapters  has  been  altered,  and  con- 
siderable additional  matter  has  been  added. 

The  introduction  to  qualitative  chemical  analysis  has 
been  discarded  in  order  to  prevent  increase  in  size  of  the 
book. 

Some  less  frequently  occurring  operations  are  outlined 

in  a  brief  appendix. 

D.  S. 

University  of  London  King's  College, 
November,  1914. 


PREFACE  TO  THE  FIRST  EDITION 

This  little  book  is  a  brief  summary  of  the  course  of  practical 
lecture-demonstrations  given  to  the  D.P.H.  class  at  King's  College, 
London.  Its  intention  is  to  put  in  the  hands  of  students  working 
in  laboratories  of  Public  Health  a  short  outline  of  the  more 
important  matters — chemical,  ph3'sical,  etc. — discussed  at  practical 
examinations  in  Sanitar}'  Science. 

The  methods  described  are  few,  but  it  is  hoped  they  will  be  found 
reliable.  It  is  felt  that  where  a  large  field  must  be  cultivated  in  a 
limited  time,  it  is  better  to  use  a  few  tools  which  have  been  well 
tried.  Whilst  going  through  the  work,  the  student  will  do  well  to 
constantly  refer  to  elementary  up-to-date  textbooks  in  the  subjects 
of  experimental  physics,  systematic  organic  and  inorganic  chemistry, 
analytical  chemistr}-,  geology,  and  bacteriolog3^  Further,  it  will 
be  necessary  for  him  at  the  outset  to  bear  in  mind  that  no  amount 
of  theoretical  reading  can  be  made  a  substitute  for  the  laborious 
and  constant  use  of  the  test-tube,  microscope,  etc.,  which  must 
take  place  at  the  benches. 

A  short  account  of  the  preparation  of  the  standard  solutions 
referred  to  in  the  work,  and  a  few  brief  notes  on  the  general 
chemical  reactions  of  the  more  commonly  occurring  metals  and 
acids,  are  set  out  in  an  appendix. 


D.  S. 


King's  College, 

November,  1905. 


CONTENTS 

CHAPTER  PA(;E 

I.    GENERAL    OBSERVATIONS    UPON    POTABLE    WATERS  IN  RELA- 
.       TION    TO    THEIR    SOURCE,    AND    METHODS    OF    EXAMINATION 

ADOPTED    FOR    SAFEGUARDING    THEIR    PURITY  -  -  I 

II.    THE    PHYSICAL    EXAMINATION    OF    WATER           -  -  -  7 

III.  THE    CHEMICAL    EXAMINATION    OF    WATER         -  -  -12 

IV.  ORGANIC    MATTER   IN    WATER                     -                  -  -  -  38 
V.    OXIDIZED    NITROGEN NITRITES    AND    NITRATES  -  -  5I 

VI.    GASES    IN    WATER WATER    SEDIMENT INTERPRETATION    OF 

RESULTS    OF    CHEMICAL   ANALYSES  -  -  -  -  60 

VII.    THE   BACTERIOLOGY   OF   WATER EXAMPLES  OF  WATERS  FROM 

VARIOUS    SOURCES    -  -  -  -  -  -         83 

VIII.    SEWAGE    EFFLUENTS    -  -  -  -  -  -97 

IX.    SOIL       --------       105 

X.    AIR  --------       118 

XI.    FOODSTUFFS:    MILK BUTTER CHEESE CEREALS — BREAD 

MEAT ALCOHOLIC    BEVERAGES LIME   AND    LEMON    JUICES 

VINEGAR MUSTARD PEPPER  —  SUGAR TEA  — COFFEE 

COCOA  -------       i^g 

XII.    DISINFECTANTS  -  -  -  -  -  -      287 

APPENDIX  -  -  -  -  -  -  -      313 

INDEX  -  -  , _  -  -  _  _      221 


LIST   OF   ILLUSTRATIONS 


FIG. 

I. 

2. 
3. 


23- 
24. 

25- 
20. 

27- 
28. 
29. 

31- 
32. 
33- 
34- 
35- 
3^- 
37- 
3«- 
39- 
40. 
41. 
42. 

43- 
44. 

45- 

46. 

47- 
48. 


Geological  fault,  etc.  - 
Curve  of  ground  water 
Diagrammatic    scheme    of 
organic  pollution  under- 
going purification 
Thresh's  apparatus     - 
22.  Objects  found  in  water 
sediments      -     69,  70,  71, 

73.  74.  75.  76.  77 
Adeney's  apparatus   - 
Barometer      and      vernier 

scales     -         -         .         - 
Hempel's  gas  burette  and 

absorption  pipette  - 
Apparatus    used     in    milk 

analysis  ... 

Apparatus    used     in    milk 

analysis  .         -         . 

Apparatus   used    in   butter 

analysis  .         .         - 

Granules  of  wheat  starch   - 
Granules  of  barlej* 
Granules  of  rye 
Granules  of  rice 
Granules  of  oat 
Granules  of  maize 
Granules  of  sago 
Granules  of  tapioca    - 
Granules  of  pea 
Granules  of  haricot  bean    - 
Granules  of  arrowroot 
Granules  of  potato 
Vibrio  tritici 

Bruchus  pisi       -  -  - 

Acarus  farinae     - 
Penicillium  glaucum  - 
Aspergillus  glaucus     - 
Mucor  mucedo  - 
Peronospora       -         -         - 
Ustilago  segetum 


PAGE 

FIG 

4 

49. 

5 

50- 

40 

5t- 

61 

52. 

72. 

53- 

.78 

54- 

103 

55- 

121 

56. 

131 

57- 

I  58 

58. 

59. 

160 

00. 

61. 

1S6 

62. 

215 

63- 

215 

64. 

216 

65. 

216 

66. 

217 

217 

67. 

218 

68. 

218 

69. 

219 

70. 

219 

220 

71- 

220 

72. 

221 

73- 

221 

74- 

221 

75- 

222 

76. 

222 

77- 

222 

222 

78. 

223 

79 

Tilletia  caries   (Uredo  foe- 

tida)       -         .         .         . 

Wheat-stem   infected   with 

puccinia  -         .         - 

Portion    of    Fig.    50    more 

highly  magnified     - 
Teleutospores     -         -         . 
.iEcidium  berberidis   - 
Gonidiospores  and  teleuto- 
spore      -         -         -         - 
Ergot  in  rye       -         -         . 
Sclerotium  -  bearing     stro- 
mata      -         -         -         . 
Stroma     containing     asco- 
carps      -         -         -         - 
Ascocarp  containing  asci    - 
Ascus  containing  ascospores 
Head  of  cysticercus   - 
Taenia  solium     -         -         - 
Trichina  spiralis 
Head  of  Distoma  hepaticum 
Ascarus  lumbricoidcs 
Oxyuris  vermicularis 
Apparatus  used  in  estima- 
tion of  alcohol 
Cells  of  cuticle  of  mustard  - 
Black  pepper     -         -         - 
Cuticle  of  tea-leaf 
Idioblasts  in  section  of  tea- 
leaf         -         -         -         - 
Tea-leaf     -         -         -         - 
Elder-leaf  -         -         -         - 
Willow-leaf         -         -         . 
Sloe-leaf     -         -         -         - 
Cuticle  of  tobacco-leaf 
Coffee-berry        ... 
Ground  coffee,  showing  cell  3 
of  testa  -         -         -         - 
Lacteal  vessels  of  chicory  - 
Dotted  vessels  of  chicorv  - 


PRACTICAL  SANITARY  SCIENCE 


CHAPTER  I 

GENERAL  OBSERVATIONS  UPON  POTABLE  WATERS  IN 
RELATION  TO  THEIR  SOURCE,  AND  METHODS  OF 
EXAMINATION  ADOPTED  FOR  SAFEGUARDING  THEIR 
PURITY 

Water  is  often  the  vehicle  of  infectious  diseases,  poisonous  metalhc 
salts,  and  a  large  number  of  undesirable  materials — animal,  vege- 
table, and  mineral.  When  we  consider  how  drinking  waters  are 
obtained,  and  how  liable  they  are  to  contamination  at  all  points 
from  source  to  final  distribution,  it  will  be  readily  admitted  that 
every  potable  water  should  be  the  object  of  the  most  careful, 
intelhgent,  and  constant  concern.  The  primary  object  of  a  water 
analysis  for  public  health  purposes  is  to  ascertain  whether  or  not 
it  contains  sewage,  as  in  the  organic  matter  contributed  by  sewage 
are  found  the  organisms  of  infectious  disease,  such  as  Bacillus 
typhosus,  Vibrio  cholercB  asiaticce,  etc.  All  other  information  is  of 
very  secondary  import  compared  with  this.  The  detection  of  or- 
ganic filth,  whether  of  animal  or  vegetable  origin,  and  of  harmful 
inorganic  matters,  when  in  small  quantities,  is  often  a  work  of  no 
little  difficulty.  In  certain  cases  where  a  small  amount  of  sewage 
containing  pathogenic  micro-organisms  finds  its  way  into  a  water- 
supply,  no  chemical  analysis,  however  delicate,  can  furnish  evidence 
of  the  pollution.  So  also  in  other  cases  the  most  exact  bacterio- 
logical examination  may  wholly  fail  to  discover  a  dangerous  water. 
The  well-informed  analyst  will  not  pin  his  faith  to  one  method  of 
examination  to  the  partial  or  total  exclusion  of  others,  but  will 
welcome  all  reliable  methods  that  can  assist  in  throwing  light  on  his 
search. 

I 


2  PRACTICAL  SAXITAJRY  SCIENCE 

At  present  four  mithods  of  examination  are  utilized — viz.. 
Physical,  Chemical,  Biological,  Bacteriological — each  of  which  has 
its  place  and  its  limits. 

The  physical  examination  may  detect  pollution  so  gross  that 
further  inquiry  is  unnecessary. 

The  chemical  analysis  can  render  no  information  concerning 
liability  to  contamination,  and  is  useless  in  detecting  small  quanti  - 
ties  of  sewage.  A  systematic  chemical  analysis  is  of  value  in  demon- 
strating variations  in  character  produced,  for  example,  by  the 
lowering  of  the  level  of  well  waters,  by  change  in  rainfall,  action 
on  lead,  iron,  and  zinc,  in  pipes,  mains,  cisterns,  boilers,  etc.  Wher^' 
the  estimation  of  sahne  constituents  must  be  determined  for  health 
purposes,  manufacturing  and  engineering  purposes,  etc.,  th*; 
chemical  method  alone  is  of  value.  Here  it  may  be  stated  as  a 
general  principle  that  waters  most  suitable  for  domestic  purposes 
are  also  most  suitable  for  manufacturing  and  engineering  purposes. 
Acid  waters  corrode  boilers,  so  do  waters  containing  marked 
quantities  of  MgCL  and  CaCl.,,  as  these  chlorides  at  high  tempera- 
tures decompose,  forming  HCl,  which  at  once  attacks  the  iron. 
CaS04,  being  insoluble,  is  deposited  as  a  crust.  CaCOg  and  MgCO;} 
together  with  salts .  of  Fe  render  water  unsuitable  for  tanning, 
dyeing,  paper-making,  and  other  industries,  owing  to  their  great 
insolubilit3^  whereby  particles  are  left  in  the  fabrics. 

Neutral  and  alkaline  (Na^COg)  waters  are  best  suited  for  boilers. 

Special  chemical  analyses  are  required  in  dealing  with  medicinal 
waters. 

By  careful  and  systematic  study  of  the  lower  forms  of  animal 
and  vegetable  life,  much  information  may  be  acquired  as  to  the 
source  and  mode  of  entry  of  surface  waters  into  water-supplies. 
Such  biological  examination  has  not  had  in  this  country  the  atten- 
tion it  deserves. 

Where  the  question  of  infective  micro-organisms  in  water  arises, 
which  to  the  sanitarian  is  of  all  questions  the  most  important,  the 
bacteriological  examination  only  can  afford  positive  evidence. 

The  examination  of  the  source  of  a  water-supply  is  of  the  hrst 
import,  and  should  never  be  omitted.  Personal  inspection  of  the 
catchment  area,  all  streams  arising  therefrom,  and  all  feeders  of 
such  streams,  should  be  made  in  situ,  and  the  relations  of  these 


GENERAL   OBSERVATIONS   UPON  POTABLE  WATERS      3 

to  possible  sources  of  pollution  carefully  noted.  When  the  gathering 
ground  has  been  thoroughly  investigated,  attention  should  be 
turned  to  the  storage  reservoirs,  and  finally  the  efficiency  of  filtra- 
tion should  be  bacteriologically  tested.  Such  examination  pre- 
supposes an  intimate  knowledge  of  the  entire  area  set  apart  for 
collection,  which  should  be  protected  from  all  possibility  of  con- 
tamination from  manured  soil,  house  drainage,  and  storm  waters. 
A  good  working  knowledge  of  the  geology  of  the  district  is  essential, 
and  every  student  of  water  analysis  should  intimately  cultivate 
the  solid  and  drift  maps  of  the  Ordnance  Survey. 

The  following  brief  table  gives  an  outhne  of  the  more  important 
strata  in  this  country,  detailed  descriptions  of  which  will  be  found 
in  any  textbook  of  geology. 

Post-tertiary  deposits : 

Alluvium,  sands,  gravels,  boulder  clay. 

Tertiary  deposits: 

Sands  of  the  Eastern  Enghsh  counties. 
Bagshot  sands  (upper,  middle,  and  lower). 
London  clay. 

Secondary  deposits: 

Chalk. 

Greensands — upper  and  lower — with  gault  lying  between., 

Weald  clay. 

Purbeck  marble. 

Kimmeridge  clay. 

Oolite. 

Lias. 

New  red  sandstones. 

Primary  deposits: 

Coal,  ironstones. 

Limestone. 

Old  red  sandstones. 

Shales  and  slates. 

Crystalline  rocks. 

Shallow  wells  sunk  in  the  post-tertiary  sands  and  gravels  are 
very  liable  to  pollution. 

The  Bagshot  sands  yield  a  fairly  soft  water. 

The  London  clay  is  an  impervious  stratum,  and  the  waters  rest- 
ing immediately  on  it  are  generally  hard. 


4  PRACTICAL  SANITARY  SCIENCE 

The  chalk  formations  of  England,  which  are  extensive,  yield 
both  hard  and  soft  waters.  The  hardness  is  mostly  temporary. 
Fissures  make  it  possible  for  pollution  to  readily  get  access  to  these 
waters. 

The  greensands,  especially  the  lower,  bear  waters  rich  in  calcium 
and  iron  salts. 

Oolites  produce  waters  almost  identical  with  those  of  the  chalk. 

The  magnesium  limestones  (dolomite)  and  new  red  sandstones 
give  origin  to  much  hardness,  of  which  a  large  portion  is  per- 
manent. 

Slates  and  igneous  rocks,  being  practically  insoluble,  3'ield  waters 
destitute  of  saline  matters,  and  are  consequently  very  soft. 


Impermeahle 
Stratum. . 

Water  hearing 
S>tratanv 


ImpermeabLe 
Stratum. . 


Fault . 


Fig. 


The  drainage  area  of  a  well  depends  upon  the  depth  of  the  well, 
the  porosity  of  the  soil  and  subsoil,  direction  of  flow  of  ground  water, 
and  the  daily  depression  produced  by  pumping.  It  may  be  con- 
sidered as  the  base  of  a  cone  whose  apex  is  the  water-level  in  the  well. 

Even  with  a  good  knowledge  of  the  geology  of  the  catchment 
area  and  districts  through  which  the  water  passes,  the  analj'st  is 
subject  to  pitfalls  at  all  points.  Strata  may  contain  caverns  and 
fissures  which  lodge  pollution  in  the  most  unlikely  positions. 
Geological  faults  account  for  unexpected  positions  of  springs. 
Where  a  water-bearing,  permeable  stratum  intervenes  between  two 
impermeable  strata,  and  a  fault  occurs,  the  imprisoned  fluid  may 
become  subject  to  such  pressure  that  it  escapes  at  the  surface  with 
tremendous  force. 


GENERAL  OBSERVATIONS   UPON  POTABLE  WATERS       5 

It  is  to  be  noted  that  the  curve  of  the  ground  water  near  the  well 
is  steep,  but  rapidly  shades  off  into  the  horizontal.  It  is  obvious 
that  with  different  types  of  soil  the  form  of  this  curve  changes 
as  the  surface  water  in  the  well  is  lowered.  The  drainage  area 
increases  in  direct  proportion  to  the  porosity. 

This  area  should  be  protected  from  all  forms  of  organic  pollution, 
including  cultivated  soils,  and  it  has  been  laid  down  as  a  minimum 
requirement  that  it  should  have  a  radius  of  twenty  times  the 
maximum  depression  of  the  water  through  pumping — e.g.,  if  the 
depression  in  the  well  be  5  feet,  the  area  should  have  a  radius  of 
100  feet,  etc.  Outside  this  cone  it  is  considered  that  filtration  is 
so  slow  that  purification  is  complete.     A  wide  margin,  however, 


Drainage     Area 


Fig.  2. 


should  be  allowed  in  the  drainage  area  to  meet  the  effects  of  in- 
creased rainfall,  possible  faults  in  the  brickwork  of  the  well,  and 
other  factors,  so  that  wells  supplying  drinking  waters  should  be 
removed  widely  from  all  sources  of  drainage,  farmyard  manure,  etc. 
A  slight  acquaintance  with  the  situations  of  many  rural  wells  in 
this  country  must  call  forth  unqualified  condemnation.  There  is 
no  doubt  that  many  epidemics  of  typhoid  fever  have  their  origin 
in  the  waters  of  these  wells.  It  is  a  matter  of  little  difficulty  to 
determine  whether  or  not  leakage  from  the  immediate  surroundings 
takes  place  into  a  well,  and  an  alkaline  solution  of  fluorescin,  an 
emulsion  of  Bacillus  prodigiosus,  or  a  concentrated  solution  of 
NaCl,  poured  around  its  mouth  and  thoroughly  washed  into  the  soil, 
will  afford  the  necessary  evidence  within  a  limited  time. 
Peat  which  lies  for  the  most  part  on  igneous  rocks  imparts  to 


6  PRACTICAL  SANITARY  SCIEXCE 

water  certain  organic  acids  capable  ot  dissolving  metals.  Wherever 
possible  such  waters  should  be  cut  out  of  a  supply.  If  this  cannot 
be  done  the  acids  should  be  neutralized  before  the  waters  pass  to 
the  consumer. 

Rivers  and  streams  from  which  water-supplies  are  procured 
should  be  scrupulously  preserved  from  the  entrance  of  pollution, 
with  a  special  view  to  the  exclusion  of  infective  bacteria.  All  river 
water  should  be  sedimented  and  filtered  before  use,  and  the  efftciency 
of  filtration  should  be  constantly  tested  by  bacteriological  examina- 
tion. 

All  forms  of  animal  and  vegetable  life  should  be  excluded  from 
service  reservoirs,  cisterns,  mains,  etc.  It  is  well  known  that 
certain  low  vegetable  forms,  especially  when  dead,  give  origin  to 
offensive  odours. 

Water  moves  in  a  cycle.  Evaporation  produces  clouds,  which 
return  to  the  earth  as  rain.  This  rain,  according  to  the  nature  of 
the  soil,  subsoil,  and  rocks,  pursues  various  paths.  If  it  fall  on 
impervious  granite  it  runs  off  in  large  quantity;  a  part  may  be 
evaporated,  and  this  will  occur  to  the  greatest  degree  during  dr3^ 
hot,  and  windy  w^eather.  If  it  fall  on  sandy  soil  a  large  proportion 
percolates,  and  the  more  porous  and  deep  the  sand,  the  more 
rapidly  and  deeply  the  water  sinks  into  the  earth.  When  it  meets 
with  an  impermeable  stratum  its  further  course  is  directed  by  the 
slope  and  contour  of  this  stratum.  Should  the  latter  take  the  form 
of  a  basin  the  w^ater  will  accumulate  until  it  overflows  the  lip  of  the 
basin,  forming  a  spring  at  a  point  where  the  stratum  outcrops. 
Again,  if  the  stratum  form  an  inclined  plane,  as  on  the  sides  of  a 
river  vallev,  the  water  will  flow  along  the  plane  to  its  outlet  at  the 
lowest  point.  Such  pure  waters  may  be  intercepted  before  reach- 
ing polluted  rivers  by  sinking  wells  at  the  bases  of  the  hills  forming 
the  sides  of  the  river  valleys.  Ihe  upper  surface  of  this  mass  of 
moving  ground  water  is  indicated  by  the  level  of  the  water  in  super- 
ficial wells.  This  surface  is  not  necessarily  horizontal.  It  is  in 
constant  motion,  travelhng  towards  the  outflow,  and  the  rate  of 
movement  is  governed  by  the  porosity  of  the  soil,  slope,  nature  of 
outlet,  etc.  An  intimate  knowledge  of  the  entire  history  of  a  water 
will  often  be  necessary  to  an  intelligent  comprehension  of  certain 
analytical  data. 


CHAPTER  II 

THE  PHYSICAL  EXAMINATION  OF  WATER 

The  physical  examination  comprises  a  determination  of  the  tur- 
bidity, colour,  odour,  and  taste.. 

Turbidity. — Pure  waters  are  free  from  visible  particles  in 
suspension:  the  slightest  degree  of  opacity  should  render  a  water 
suspicious.  On  the  other  hand,  the  most  transparent  and  brilliant 
waters  may  contain  the  most  pronounced  pollution.  Turbidity 
may  be  produced  by  access  of  the  contents  of  cesspools,  drains, 
manure  heaps,  and  surface  refuse  of  all  types,  especially  after  rains, 
when  it  forms  often  the  worst  kind  of  pollution.  It  may  be  pro- 
duced by  particles  of  clay,  iron,  chalk,  etc.,  when  a  chemical  and 
microscopical  examination  may  be  necessary  to  disclose  the  nature 
of  the  matter  in  suspension.  Waters  containing  iron  very  often 
deepen  in  opacity  during  the  first  day  or  two  after  collection,  owing 
to  the  formation  of  persalts  of  that  metal,  which  are  highly  insoluble. 
Such  opacity  immediately  disappears  on  the  addition  of  a  small 
quantity  of  dilute  HCl. 

Estimation  of  Turbidity.  —  Place  the  Winchester  on  a  white 
porcelain  tile  in  a  good  north  light,  and  examine  it  carefuUy 
with  the  naked  eye.  Much  information  regarding  opacity,  sedi- 
ment, etc.,  may  thus  be  gained  by  a  practised  eye. 

The  sample  may  be  described  as  brilliant  (aeration  good),  clear, 
slightly  turbid  or  opalescent,  turbid,  markedly  turbid.  To  estimate 
the  quantity  of  matter  in  suspension,  filter  lOO  c.c.  through  a  hard 
filter  and  evaporate  in  a  platinum  dish  to  dryness.  The  difference 
between  the  weight  of  the  residue  dried  at  ioo°  C.  and  that  of  loo  c.c. 
of  the  unfiltered  sample  similarly  treated  will  represent  the  desired 
result.  Or,  where  a  centrifugal  machine  is  available,  by  means  of 
small  tubes  the  sediment  may  be  read  off  quantitatively  on  a  gradu- 

7 


8  PRACTICAL  SANITARY'  SCIENCE 

ated  scale.  The  amount  of  light  permitted  to  pass  through  a  cohimn 
of  opalescent  water  mounted  in  a  glass  cylinder  can  be  matched 
by  the  illumination  of  a  polarized  light  ray  passing  through  a 
second  similar  glass  cylinder  containing  no  water;  the  degree  of 
rotation  of  the  Nicol  of  the  eyepiece  expresses  the  degree  of 
turbidity. 

Coloup. — Uncontaminated  rain  water  presents  a  pale  blue  tint 
in  the  '  two-foot  '  tube.  Yellow  tints  point  to  organic  matter, 
brownish-red  suggest  a  peaty  origin,  and  reddish-yellow  indicate 
iron.  Any  appreciable  shade  of  yellow  or  brown  will  excite  sus- 
picion, and  lead  to  a  careful  search  for  the  cause.  Colour  tables 
have  been  formulated  for  the  use  of  water  analysts,  but  do  not 
seriously  assist  a  trained  eye. 

Clean  thoroughly  and  fill  the  '  two-foot  '  tube ;  place  it  on  the  tile ; 
look  down  through  the  column,  noting  the  tint  of  colour,  which  may 
range  from  a  pale  sky-blue  to  a  3^ellow  or  brown. 

As  to  colour,  for  all  ordinary  purposes  the  naked-eye  inspection 
is  sufficient,  but  if  for  any  reason  great  accuracy  is  required  a  tinto- 
meter may  be  used.  Two  hollow  glass  wedges  containing  respec- 
tively dilute  solutions  of  CUSO4,  and  a  mixture  of  ferric  and  cobalt 
chlorides  slightly  acidified,  are  made  to  slide  over  each  other  in 
front  of  an  empty  tube,  so  that  any  desired  combination  of  blue 
and  brown  tints  can  be  obtained.  Alongside  is  placed  a  similar 
tube  filled  with  the  sample,  and  the  wedges  are  arranged  so  that  on 
looking  down  upon  a  white  surface  the  colours  exactly  match.  The 
prisms  are  graduated  in  millimetres,  and  the  results  are  expressed 
in  terms  of  millimetres  of  blue  and  brown. 

Water  may  be  variously  coloured  by  algae  and  other  vegetable 
organisms.  Crcnothrix  polyspora  (rich  in  iron)  colours  it  red  or 
reddish-brown,  and  decomposing  accumulations  of  the  dead  or- 
ganism may  produce  serious  nuisance.  Green  and  blue  algse  produce 
their  respective  tints,  and  peat,  according  to  its  concentration,  all 
shades  of  brown. 

Odour. — Drinking  water  should  be  free  from  all  odour.  Dis- 
solved gases  may  be  liberated  by  slightly  warming  the  water,  say 
to  a  temperature  of  37°  C.  In  the  case  of  peaty  waters  it  has  been 
found  at  times  that  even  after  the  most  careful  filtration  a  slight 
odour  still  attaches  to  the  water.     For  many  reasons  peaty  waters 


THE  PHYSICAL  EXAMINATION  OF  WATER  9 

do  not  furnish  good  supplies,  and  where  other  sources  are  available 
should  be  passed  over. 

River  waters  usually  have  a  faint  smell,  due  to  a  variety  of  causes, 
most  often,  perhaps,  to  vegetable  organisms,  some  of  which^ — e.g., 
the  well-known  sewage  fungus — are  associated  with  the  production 
of  HgS. 

The  dead  and  decomposing  remains  of  plants  and  animals  furnish 
a  variety  of  odours,  not  only  in  river  waters,  but  in  cisterns,  reser- 
voirs, and  mains.  Of  late  years  attention  has  been  called  to  distinct 
species  of  lowly  vegetable  forms  which  produce  disagreeable  odours 
in  water. 

It  is  customary  to  obtain  the  sample  of  water  for  physical  exam- 
ination from  the  vessel  containing  that  for  the  chemical  examina- 
tion, and  something  may  now  be  said  respecting  the  mode  of  collect- 
ing such  samples.  The  so-called  '  Winchester  '  quart  bottle  has  long 
been  used  for  this  purpose,  and  when  made  of  colourless  glass 
answers  the  purpose  admirably.  The  bottle  should  be  thoroughly 
cleansed  by  rinsing  with  dilute  HCl,  and  afterwards  removing  the 
last  trace  of  acid  with  distilled  water.  Where  it  has  to  be  sent  by 
rail,  etc.,  it  is  packed  in  a  tightly-fitting  wicker  case  or  wooden 
box  fitted  with  padlock.  Before, filhng,  the  bottle  should  be  rinsed 
with  a  portion  of  the  sample.  A  little  air  space  should  be  left  under 
the  stopper  to  avoid  cracking  of  the  neck  through  rise  of  tempera- 
ture. Procedure  in  collection  will  vary  according  to  the  object  of 
the  examination..  If  it  is  desired  to  ascertain  whether,  for  example, 
lead  is  dissolved  by  a  water  in  the  house-pipes,  it  will  be  necessary 
to  collect  the  first  runnings  from  the  taps  in  the  morning.  When 
a  bacteriological  examination  is  required,  a  special  method  must  be 
pursued,  which  will  be  described  later.  Where  the  sample  is  to  be 
taken  from  a  river,  cistern,  etc.,  the  bottle,  prepared  as  above,  is 
usually  immersed  some  little  distance  below  the  surface,  where  the 
stopper  is  removed  and  the  bottle  filled.  A  small  portion  is  poured 
out  in  order  to  procure  the  air  space  mentioned,  and  the  stopper 
inserted.  Various  forms  of  apparatus  have  been  devised  for  collect- 
ing samples  under  different  conditions,  but  the  circumstances  will 
in  all  cases  suggest  the  mode  of  procedure,  if  it  be  kept  in  mind 
that  a  fair  sample  of  the  water  as  it  is  usually  found  is  the  object 
desired. 


u>  PRACTICAL   SANITARY  SCIENCE 

A  correct  record  of  the  sampling  process,  etc.,  should  be  made  on 
the  spot,  and  attached  as  a  label — 

1.  Date,  time,  and  place  of  taking  sample. 

2.  Depth  below  surface,  state  of  water-level — high.  low,  or 
average. 

3.  Particulars  of  rainfall  and  of  geological  strata  of  district. 

4.  Depth  of  water-level  below  ground-level. 

5.  Description  of  surroundings,  possible  sources  oi  pollution,  such 
as  sewers,  cesspits,  cemeteries,  etc. 

In  many  cases  it  is  well  for  the  analyst  to  supply  his  own  collect- 
ing-bottle, with  instructions  for  taking  the  sample  and  filling  up  the 
label.  The  sender  should  be  made  to  understand  that  the  specimen 
must  be  of  the  same  nature  exactly  as  that  actually  consumed,  and 
that  it  is  desired  to  ascertain  the  maximum  degree  of  ])o]lution  that 
may  at  any  time  obtain.  All  such  particulars,  as  also  the  results 
of  the  analysis,  should  be  transcribed  into  a  book  and  preserved  for 
future  reference. 

Estimation  of  Odour.  —  Place  250  c.c.  in  a  stoppered  flask, 
and  heat  to  37°  C.  in  an  air-bath.  Remove  the  stopper  and 
smell.  It  is  generally  sufficient  to  shake  the  sample  well  in  the  cold, 
rapidly  remove  the  stopper,  and  smell.  The  variety  of  odours  is 
inhnite.  Many  odours  are  produced  by  organisms,  either  as  products 
of  their  life-history  or  of  their  death  and  putrefaction.  Beggiatoa, 
Chara,  and  certain  species  of  Crenothrix  produce  an  offensive  odour 
of  H.,S.  It  is  believed  that  Beggiatoa  during  its  life-cycle  reduces 
sulphates,  and  produces  under  favourable  circumstances  large 
quantities  of  H.,S.  Crenothrix,  moreover,  often  produces  abundance 
of  colour,  varying  from  brown  to  red.  Tabellaria,  Meridion,  and 
certain  diatoms,  as  also  the  protozoon  Cryptomonas,  furnish  a  dis- 
tinctl}'  aromatic  odour.  A  lishy  odour  is  produced  by  Volvox  and 
the  protozoa  O^cnodinium,  Bursaria,  and  Uroglena.  A  grassy 
odour  accompanies  Rivularia,  Anabsena,  and  Caelosphserium. 

Taste. — Pure  rain  water  well  aerated  has  a  fairly  distinctive 
taste,  more  easily  appreciated  than  described.  So  also  have  peaty 
waters,  sea  water,  and  chalybeate  waters.  The  taste  of  a  particular 
sample  may  be,  however,  everything  to  be  desired,  whilst  the  water 
is  the  foulest  of  the  foul.  Taste,  however,  is  of  little  service  to  the 
analyst,  and  not  always  to  be  recommended.     Iron  is  about  the 


THE  PHYSICAL  EXAMINATION  OF  WATER  ii 

only  ingredient  that  can  in  this  way  be  detected  in  very  small  quan- 
tities, being  recognisable  to  the  amount  of  0-5  part  per  100,000. 

Potable  waters  have  been  classified  as — 

Wholesome.— {1)  Spring  water;  (2)  deep- well  water;  {3)  upland 
surface  water. 

Suspicious.— {^)  Stored  rain  water;  (5)  surface  water  from  culti- 
vated land. 

Dangerous.— [6)  River  water  polluted  with  sewage ;  (7)  shallow- 
well  water. 


CHAPTER  III 

THE  CHEMICAL  EXAMINATION  OF  WATER 

It  will  be  well  for  the  student  from  the  lirst  to  ht  up  his  own  appa- 
ratus, and  make  his  own  standard  solutions.  He  must  learn  to 
use  properly  the  chemical  balance,  and  a  special  demonstration  is 
devoted  to  the  mechanism,  methods  of  adjusting  and  using  this 
all-important  instrument.  Before  commencing  to  weigh,  he  should 
see  that  the  balance  is  accurately  levelled,  and  that  the  index  moves 
without  effort  over  the  whole  field  of  the  graduated  scale,  and  comes 
to  rest  at  zero.  All  weights,  basins,  etc.,  should  be  transferred  to 
and  from  the  scale-pans  only  when  these  are  supported.  It  is 
customary  to  use  three  rows  of  weights,  grammes  (brass),  deci- 
grammes and  centigrammes  (platinum),  and  milligrammes  (plati- 
num). A  rider  of  platinum  applied  to  the  beam  also  reads  milli- 
grammes. The  right-hand  pan  should  be  used  only  for  weights, 
and  these  should  be  placed  methodically  in  three  rows  in  front  of  the 
operator.  By  this  means  the  total  reading  is  most  easily  obtained 
and  checked. 

Immediately  on  finishing  a  weighing  all  weights  should  be  trans- 
ferred to  the  box,  with  the  forceps  used  for  the  purpose,  and  the  box 
and  balance  carefully  closed. 

The  standard  solutions  in  use  in  water  analysis  are  of  two  types : 

1.  Normal,  decinormal,  centinormal,  etc. 

2.  Standards  of  such  strength  that  a  litre  contains  the  equivalent 
of  a  gramme,  or  submultiple  of  a  gramme,  of  the  substance  to  be 
estimated. 

A  standard  solution  is  said  to  be  normal  when  one  litre  contains 
the  equivalent  weight  in  grammes  of  an  element,  acid,  alkali,  or 
salt. 

The  molecular  weight  of  HCl  is  36-35;  therefore  36-35  grammes 
HCl  per  litre  =  normal  HCl,  written  N.HCl. 


THE  CHEMICAL  EXAMINATION  OF  WATER  13 

In  like  manner  N.NaOH=  40  grammes  per  litre. 
Since  the  term  '  equivalent '  signifies  the  weight  in  grammes  of  the 
substance  under  consideration,  which  is  chemically  equivalent  to 

1  gramme  of  H,  normal  H2S04=      =49  grammes  per  litre. 

A  decinormal  solution  {—)  is  one-tenth  the  strength  of  a  normal 
— thus  3~j-  NaOH=4  grammes  per  litre — and  a  seminormal  (^)  and 
centinormal  (y^jj)  are  respectively  one-half  and  one-hundredth  the 
strength  of  the  normal — viz.,  20  grammes  and  0-4  gramme  per  litre 
respectively. 

In  tribasic  acids  one-third  of  the  molecular  weight  in  grammes 
per  litre  constitutes  a  normal  solution,  and  so  on  for  acids  of  higher 
basicity. 

The  terms  '  normal,'  '  decinormal,'  etc.,  are  used  sometimes  with  a 
different  meaning.  Permanganate  of  potassium,  as  we  shall  see 
presently,  in  acid  solution  is  reduced  by  many  substances,  accord- 
ing   to    the    equation    KgMn.Pg  =  KgO  +  2MnO  -t-  O5,    in   which 

2  gramme  molecules  of  KMn04  correspond  to  5  gramme  molecules 

of  oxygen  or  to  10  gramme  molecules  of  hydrogen.     Accordingly, 

in  order  to  put  permanganate  of  potassium  on  a  hydrogen  basis,  a 

1     1  X-      ■         J    .         X  ■    316-3  /2KMn04\  r 

normal  solutionis  made  to  contain  - — - =  31' 03  grammes 

10    V       10      /  ^ 

per  litre.     In  the  same  way  K2Cr207.  which  in  acid  solution  parts 
with   O3,  requires   for   a  normal  solution  -^ —  (    ^a^    ^)  =  49'^ 

grammes  per  litre. 

The  second  type  of  standard  solution  used  is  constructed  so  that 
a  minimum  amount  of  calculation  suffices  in  estimating  results. 
Since  it  is  customary  to  represent  the  various  items  of  the  analysis 
as  parts  by  weight  per  100,000  of  the  water,  and  since  i  c.c.  of  water 
weighs  I  gramme  (1,000  milligrammes),  100  c.c.  of  water  will  weigh 
100,000  milligrammes. 

It  is  therefore  convenient,  when  possible,  to  work  on  100  c.c.  of 
the  water  sample  throughout  the  various  estimations,  and  to  use  a 
standard  solution  that  will  give  readings  directty  in  the  above 
terms. 

Suppose  we  wish  to  estimate  the  quantity  of  CI  in  a  water,  we 
use  a  solution  of  AgNOg  of  such  strength  that  i  c.c.  is  equivalent 


14  PRACTICAL  SANITARY  SCIENCE 

to  I  milligramme  CI.  To  make  this  solution  we  refer  to  the  molec- 
ular weight  of  AgNOg,  and  the  atomic  weight  of  CI.  AgNOa-t- 
XaCl-AgCl  +  NaNOg. 

170  grammes  AgNOg  precipitate  35-35  grammes  CI. 
.-.  dividing  by  35-35,  we  find  that  4-8  grammes  AgNO.,  precipitate 
I  gramme  CI. 

If,  then,  we  dissolve  4-8  grammes  AgXO.j  in  i  litre  of  water  we 
obtain  a  solution  i  c.c.  of  which  precipitates  i  milligramme  of  CI, 
and  working  with  100  c.c.  of  water,  the  number  of  c.c.  of  the 
silver  nitrate  solution  used  indicates  the  number  of  milligrammes 
of  CI  in  100,000  milhgrammes  of  the  water,  which  is  parts  per 
100,000. 

Again,  in  estimating  XH3  a  standard  solution  of  XH4CI  is  pre- 
pared and  used  in  the  same  way. 

One  molecule  of  XH4CI  contains  i  molecule  of  XH^. 
53*35  grammes         ,,         contain  17  grammes 
and  3-14         ,,  ,,  ,,         I  gramme 

Therefore  a  litre  containing  3-14  grammes  XH4CI  will  contain 
I  gramme  NH3,  and  consequently  i  c.t.  contains  i  milligramme. 
It  is  found  convenient  to  dilute  this  100  times,  so  that  i  c.c.=  o-oi 
milligramme  XH3. 

Standard  solutions  should  be  stored  in  bottles  in  such  manner 
that  both  internal  and  external  evaporation  are  impossible.  In 
the  first  case,  where  the  bottle  is  not  quite  full,  pure  water  will 
evaporate  and  condense  on  the  upper  portions  of  the  vessel;  in  the 
second,  evaporation  will  take  place  into  the  atmosphere.  The  loss 
of  water  will  naturally  depend  on  the  substance  dissolved,  the  tem- 
perature, the  age  of  the  solution,  and  the  frequency  with  which  it 
is  used.  A  rough  estimate  may  often  be  made  of  the  probable 
amount  of  change  in  strength  by  noting  the  date  of  preparation, 
which  should  always  be  found  on  the  label.  Some  standards  undergo 
chemical  change  by  the  action  of  light,  and  should  therefore  be  kept 
in  the  dark. 

In  reading  a  burette,  arrange  it  so  that  the  lower  convex  line  of 
the  meniscus  is  in  the  same  horizontal  plane  with  the  eye;  the 


THE  CHEMICAL  EXAMINATION  OF  WATER  75 

division  of  the  scale  cut  by  the  lowest  point  of  this  convex  line  is 
the  reading. 

In  measuring  small  quantities  of  liquids  much  time  may  be  saved 
by  using  a  few  plain  10  c.c.  pipettes  graduated  to  tenths  of  a  c.c,  and 
for  quantities  under  a  c.c.  a  i  c.c.  pipette  graduated  to  hundredths. 
These  can  be  easily  and  rapidly  cleaned,  and  as  easily  and  rapidly 
manipulated,  and  may  often  take  the  place  of  burettes.  In 
weighing  platinum  and  porcelain  basins,  crucibles,  etc.,  it  is  very 
necessary  to  see  that  they  are  quite  dry.  To  insure  this,  especially 
after  heating,  they  should  be  placed  for  ten  minutes  in  a  desiccator 
immediately  before  going  to  the  balance.  It  is  also  necessary  to 
be  certain  that  all  such  vessels  are  thoroughly  clean.  Accurate 
notes  of  all  operations,  measurements,  weights,  etc.,  should  be  made 
in  the  bench  notebook,  and  considered  as  much  a  part  of  the  work 
as  the  operations  themselves.  Without  this  notebook  it  is  impos- 
sible to  get  on  with  analytical  chemistry.  Where  possible  it  is  well 
to  write  down  the  chemical  equations  representing  decompositions. 
When  in  doubt  in  this  matter  refer  to  a  work  on  chemistry.  All 
colour  matches  are  best  made  in  glass  cylinders  standing  on  a  white 
ground,  as  the  operator  faces  a  north  light. 

The  Reaction  of  Water.  —  This  is  an  important  item,  and 
should  form  the  first  step  in  the  routine  chemical  examination.  In 
addition  to  the  use  of  red  and  blue  litmus-papers,  it  is  often  well  to 
use  a  more  delicate  indicator,  such  as  phenolphthalein,  and  to  esti- 
mate the  amount  of  acidity  (when  acid)  in  100  c.c.  by  titrating  with 
-^0  NaOH,  or  of  alkalinity  (when  alkaline)  with  ^  H2SO4.  An  acid 
water  dissolves  lead,  iron,  and  zinc;  it  also  fixes  ammonia,  and  so 
prevents  its  being  distilled  off.  Some  hold  that  neutral  waters  and 
those  possessing  very  slight  temporary  hardness  are  capable  of 
dissolving  lead.  It  should  be  remembered,  however,  that  sodium 
carbonate  when  present  prevents  this  action.  Houston  has  corre- 
lated the  acidity  and  plumbo-solvency  of  a  large  number  of  moor- 
land waters. 

He  causes  the  sample  to  percolate  upwards  through  a  column 
of  specially  prepared  lead  shot  at  a  uniform  rate.  He  then 
collects  successive  50  c.c.'s,  and  estimates  the  amount  of  lead  in 
each. 

The  following  figures  are  taken  from  a  report  to  the  L.G.B.: 


I6 


PRACTICAL  SAXITARY  SCIENCE 


Acidity. 

Pl.UMBO-Soi.VENXY, 

Number  of  c.c. 

Mg 

ms.  of  I'b  in 

N  Na.iCOj  required  to  neutralise 

100  c.c. 

of  the  Water  after 

"       loo  c.c.  of  the  Water. 

Filiration 

through  Lead  Shot. 

0-2 

0-28 

0-3 

0-25 

0-4 

0-4 

0-5 

0-66 

0-6 

0-92 

0-8 

1-55 

0-95 

2-66 

1-5 

2-8 

17 

5-6 

2-2 

8-6 

Some  waters  not  acid,  and  failing  to  dissolve  lead,  exert  an 
'  erosive  '  action,  forming  an  insoluble  film  of  oxyhydrate  upon 
the  lead,  which  after  a  time  may  become  detached,  and  produce  a 
degree  of  opacity. 

Chlorides  in  Water. — Free  CI  rarel}'  occurs  in  water-supplies. 
Certain  manufacturing  effluents  ma3'  on  occasion  contain  small 
quantities  of  free  CI,  but  the  quantit}^  is  so  small  and  the  occurrence 
so  rare  that  this  form  of  CI  may  be  practically  ignored.  The  great 
bulk  of  CI  in  drinking  water  is  found  as  NaCl.  All  soils  and  sub- 
soils contain  this  salt  in  large  amounts.  The  water-bearing  strata 
are  rich  in  chlorides,  especially  NaCl,  and  consequently  rain  water 
(which  itself  may  contain  as  much  as  0-5  part  per  100,000  NaCl), 
as  it  percolates  from  the  surface  to  the  impermeable  stratum  on 
which  it  rests,  dissolves  these  in  considerable  quantities.  CaClg 
and  MgClg  are  found  in  certain  strata— chalk  and  limestone — in 
much  smaller  quantities,  but  MgCU  abounds  in  sea  water,  and  in 
large  quantity  is  distinctive  of  it.  Wells,  reservoirs,  etc.,  to  which 
sea  water  can  obtain  access  will  yield  waters  rich  in  ^MgCl,.  Sources 
of  water  subject  to  much  evaporation,  especiall}'  if  situated  near 
the  sea,  exhibit  large  quantities  of  chlorides.  The  total  CI  in  sea 
water  approaches  2,000  parts  per  100,000,  and  if  this  figure  be  kept 
in  memory  it  will  explain  the  large  estimations  often  found  some 
considerable  distance  from  the  littoral.  During  the  passage  of  water 
through  the  soil,  subsoil,  and  strata,  CI  is  not  likely  to  be  diminished 
as  are  the  organic  matter  and  bacteria. 

When  we  have  accounted  for  all  the  CI  contributed  by  rain  water, 


THE  CHEMICAL  EXAMINATION  OF  WATER  17 

sea  water,  soil,  subsoil,  and  strata,  and  trade  effluents  from  chemical 
works,  paper  factories,  etc.,  there  may  remain  a  surplus  furnished 
by  organic  pollution  of  animal  origin.  This  surplus  is  of  some 
import  to  the  analyst,  as  indicating  sewage;  but  before  it  is  returned 
as  such  all  the  possible  sources  of  origin  just  mentioned  must  be 
rigidly  excluded.  Vegetable  organic  matter  does  not  yield  this 
surplus  CI.  Attempts  have  been  made  in  U.S.A.  to  estimate  and 
permanently  record  the  CI  due  to  the  natural  causes  named,  so  that 
sewage  pollution  may  be  readily  detected.  Maps  have  been  con- 
structed and  points  furnishing  equal  quantities  of  CI  joined  by  lines 
named  '  isochlors.'  In  districts  remote  from  the  sea,  and  centres 
of  population  and  land  cultivation,  such  maps  may  be  more  or  less 
reliable,  but  in  this  country  they  would  be  useless.  MHiilst  it  is 
true  that  animal  pollution  contains  much  CI  (urine  about  i  per 
cent,  chlorides),  and  that  soils,  strata,  etc.,  in  certain  districts  yield 
fairly  constant  quantities,  still  there  are  variations  in  many  localities 
in  these  natural  sources,  and  it  is  only  where  large  quantities  of  sew- 
age have  gained  access  to  waters  that  we  can  rely  on  the  surplus 
CI  as  evidence  of  this  accession.  In  the  case  of  small  amounts  of 
sewage  this  surplus  CI  figure  is  of  little  if  any  value.  But  in  a  water 
analysis  the  most  important  information  lies  very  often  not  so  much 
in  the  exact  amount  of  a  particular  constituent  as  in  the  fact  that  its 
presence  points  to  past  pollution,  and  consequently  to  the  possibility 
and  even  probability  of  a  recurrence  of  such  pollution.  In  this 
light  CI  and  nitrates  play  an  important  role.  These  afford  unmis- 
takable evidence  of  previous  contamination;  they  are  the  distinct 
and  unchangeable  indications  of  previous  pollution,  but  as  to 
whether  recent  or  remote  they  indicate  nothing.  Hence  the  neces- 
sity for  further  and  different  forms  of  examination.  As  to  the 
amounts  of  chlorides  that  should  condemn  waters,  it  is  difficult  to 
speak,  since  there  is  such  infinite  variety  in  the  quantities  contained 
in  different  soils  and  strata.  MgClg  and  CaClg  render  waters  hard, 
so  that  more  than  4  or  5  parts  of  either  or  both  of  these  per  100,000 
will  cause  a  large  destruction  of  soap,  and  these  figures  will  in  most 
cases  form  the  limit  for  domestic  waters.  NaCl  may  go  up  to 
perhaps  50  parts  per  100,000;  above  this  it  imparts  a  taste,  and  the 
water  consequently  will  not  be  fit  for  drinking. 


i8  PRACTICAL  SAXITARY  SCIENCE 

Estimation  of  CI. 

Apparatus  and  Reagents  Required. 

A  white  porcelain  basin  capable  of  holding  250  c.c. 

A  glass  stirring-rod. 

A  burette  charged  with  standard  solution  of  AgNOa,  of  which 
1  c.c.  is  equivalent  to  i  milligramnie  CI  (4"8  grammes  AgNO.,  to  a 
litre  of  water). 

A  5  per  cent,  solution  of  KoCrOj. 

Place  100  c.c.  of  the  water  in  the  porcelain  dish. 

Add  I  c.c.  of  the  K2Cr04  solution,  and  stir. 

J\un  in  from  the  burette  drop  bj^  drop  the  silver  nitrate  solution 
until  the  pale  ^-ellow  colour  remains  permanently  orange. 

Take  the  reading. 

The  rationale  of  the  process  is  as  follows: 

AgNOg,  when  added  to  a  solution  of  chlorides,  forms  AgCl,  a 
white  curdy  precipitate  insoluble  in  HNO3,  soluble  in  NH^HO. 
Without  a  special  indicator  it  would  be  impossible  to  determine 
when  the  whole  of  this  white  precipitate  had  been  formed — when  the 
whole  of  the  CI  had  been  deposited. 

K2Cr04  is  also  acted  on  by  AgNOg,  and  Ag2Cr04  formed,  which  is 
red.  But  so  long  as  any  chloride  remains  ununited  with  Ag,  the 
silver  chromate  is  decomposed  and  AgCl  formed;  hence  the  dis- 
appearance of  the  red  colour  on  stirring.  Immediately  the  whole 
of  the  CI  is  precipitated  as  AgCl  the  red  silver  chromate  remains. 

The  reactions  are  represented  by  the  equations — 

AgNOg  +  NaCU  AgCl  +  NaNOg. 

2AgX03  +  K.,Cr04  =  Ag2Cr04  +  2KXO3. 

2NaCl  +  Ag2Cr04=2AgCl  +  Na2Cr04. 

It  is  obvious  that  the  K2Cr04  should  be  free  from  CI.  Acidity  in 
the  water  will  dissolve  Ag2Cr04 ;  hence  if  a  water  is  even  slightly  acid 
it  must  be  neutrahzed.  Freshly  precipitated  CaCOg  is  the  best  alkali 
to  use,  and  it  should  be  used  only  to  the  point  of  neutralization. 
If  too  little  K2Cr04  is  used  the  CI  reading  will  be  too  high,  and  if 
too  much  be  used  it  is  difficult  to  determine  the  end;  i  c.c,  accord- 
ingly, is  found  a  suitable  quantity  when  the  solution  is  of  the  above 


THE  CHEMICAL  EXAMINATION  OF  WATER  19 

strength.  It  will  be  noticed  that  as  the  titration  proceeds  the  red 
AggCrO^  disappears  more  slowly  on  stirring,  until  finally  it  ceases 
to  disappear.  This  is  explained  by  the,  continuous  decrease  in  the 
original  chloride.  Whilst  abundance  of  this  undecomposed  chloride 
remains  in  solution,  the  Ag2Cr04  is  rapidly  robbed  of  its  Ag  and  the 
red  colour  discharged;  but  as  the  chloride  diminishes  and  the  end 
approaches,  the  decomposition  of  the  Ag2Cr04  becomes  slower  and 
slower,  until  at  the  end  of  the  reaction  it  ceases,  and  the  red 
Ag2Cr04  permanently  remains. 

Since  the  colour-change  from  pale  yellow  to  red  is  somewhat 
difficult  to  detect  in  daylight  (it  is  more  easily  perceived  by  gas- 
light), a  flat  glass  cell  whose  plates  are  |  inch  apart  should  be  filled 
^dth  chromate  solution  of  the  same  tint  as  that  of  the  contents  of 
the  basin,  and  interposed  between  the  eye  and  the  basin  during 
titration,  when  the  appearance  of  the  red  silver  chromate  becomes 
strikingly  manifest.  The  effect  is  to  neutralize  the  yellow  and  to 
cause  the  appearance  of  the  basin  to  be  the  same  as  if  it  were  filled 
with  pure  water.  In  working  with  turmeric,  cochineal,  etc.,  cells 
should  be  used  filled  with  corresponding  solutions  of  turmeric, 
cochineal,  etc. 

The  number  of  c.c.  of  silver  nitrate  run  in  represents  the  number 
of  parts  of  CI  per  100,000. 

100  c.c.  water  =  100,000  milhgrammes, 
I  c.c.  AgN03=  I  milhgramme  CI; 
.■.  the  number  of  c.c.  AgN03  used=  number  of  parts  CI 
per  100,000  water. 

Some  operators  subtract  -i  c.c.  from  the  AgNOg  figure  as  the 
quantity  required  to  form  the  slight  permanent  orange  colour. 
Others  add  a  small  measured  quantity  of  the  water  sample  from  a 
burette  until  the  permanent  orange  tint  departs,  and  reckon  half  of 
this  with  the  AgNOg  reading. 

It  is  well  always  to  do  tw^o  careful  estimations,  and  take  the  mean. 
When  once  an  idea  of  the  quantity  of  CI  present  is  obtained,  two 
careful  estimations  can  be  performed  very  rapidly.  A  control  basin 
containing  100  c.c.  of  the  same  water  and  i  c.c.  of  K2Cr04  may  assist 
ill  determining  the  end  reaction. 

Where  small  quantities  of  CI  are  to  be  estimated,  250  c.c.  or  500  c.c. 


20  PRACTICAL  SANITARY  SCIENCE 

of  the  water  may  be  concentrated  by  evaporation  to  lOO  c.c. 
Alkaline  silicates,  nitrates,  and  phosphates  slightly  affect  the  CI 
estimation,  but  not  to  such  a  degree  as  to  require  correction. 

Chlorine   is   sometimes   returned   in   terms   of   sodium   chloride 

This  figure  is  found  bv  multiplying  the  CI  return  by  - — ~ .     WHiere 

35"35 
CaClo,  or  i\IgClo,  or  both,  enter  into  the  problem,  corrections  have 
to  be  made  in  accordance  with  the  respective  molecular  weights 
and  the  quantities  of  each  present. 

In  chalk  and  red  sandstone  waters  3  parts  of  CI  per  100,000  may 
occasion  no  suspicions  of  sewage,  and  4  or  5  parts  may  be  passed, 
unless  organic  pollution  is  indicated  by  other  items  of  the  analysis. 
Pure  surface  waters  seldom  contain  more  than  i  part  per  100,000, 
whilst  deep  greensand  waters  may  give  rise  to  15  to  20  parts  per 
100,000,  and  still  be  absolutely  pure. 

The  following  are  a  few  examples  of  the  CI  figures  for  different 
waters : 

Parts 
per  100,000. 

A  well  in  St.  Pancras       -----  4-5 

Lambeth  water-supply    -             -             -             -  -  i  -g 

.,            ,.          -               -               -               -  -  2-0 

Southwark  water-supply  -              _              .              .  -  1.85 

A  well  in  Devonshire        -              -              -              -  -  3-1 

Thames  water  at  Waterloo  Bridge           -             -  -  lo^-z 

Deep  well  near  Hindhead              _             _             .  -  ii2'3 

Sample  of  rain  water  taken  from  rain  gauge  in  Herts  -  0-3 

Hardness. 

The  hardness  (soap-precipitating  power)  of  a  water  exerts  little 
influence  on  health,  but  from  an  economic  point  of  view  is  of  some 
importance. 

A  soap  is  a  chemical  salt  formed  by  the  union  of  an  inorganic 
base  with  one  or  more  fatty  acids. 

Sodium  and  potassium  soaps  are  soluble  in  water,  and  when 
shaken  with  it  form  a  dense  froth  or  lather.  Calcium  and  mag- 
nesium soaps  are  insoluble  in  water,  and  fail  to  form  a  lather.  Hence, 
if  a  solution  of  a  soluble  soap  be  added  to  water  containing  calcium 
or  magnesium  salts,  these  last  will  be  completely  precipitated  in 
the  form  of  insoluble  calcium  or  magnesium  soaps  before  a  lather 
is  produced.     Accordingly,  by  using  a  standard  soap  solution,  an 


THE  CHEMICAL  EXAMINATION  OF   WATER  21 

approximate  estimate  of  the  quantity  of  such  soap-precipitating 
bodies  in  a  water  can  be  made.  The  total  quantity  of  such  bodies, 
as  measured  by  the  standard  soap  solution,  constitutes  the  total 
hardness.  Other  bodies  than  calcium  and  magnesium  salts  are 
occasionally  present  in  water,  which  act  in  a  similar  manner  on  soap. 
If  much  sodium  chloride  be  present,  it  will  precipitate  soap  from  its 
solution  in  an  unaltered  state. 

CaCOg  and  MgCOg,  especially  the  first,  have  by  far  the  greatest 
share  in  rendering  waters  hard.  These  salts  are  formed  in  solution 
in  the  soil  as  bicarbonates  [Ca(HC03)2  and  Mg(HC03)2]  by  COg 
dissolved  in  rain  water.  On  boiling  such  waters,  CO2  escapes,  and 
insoluble  carbonates  separate  out  as  a  precipitate — 

Ca(HC03)2-^CaC03  +  CO2  +  HgO. 

The  addition  of  slaked  lime  to  water  containing  the  bicarbonates 
of  the  alkaline  earths  results  in  the  precipitation  of  the  lime  added 
and  the  bicarbonates  thus : 

Ca(HC03)2  +  Ca(OH)2=  2CaC03  +  2H20.    (Clark's  process.) 

If  now  the  boiled  water  be  filtered,  made  up  to  its  original  volume 
with  distilled  water,  and  again  titrated  with  standard  soap  solution, 
the  permanent  hardness  is  obtained. 

The  difference  between  the  total  and  the  permanent  hardness  is 
the  temporary  hardness. 

The  soap  test  has  been  made  to  measure  the  quantity  of  CaCOg 
and  other  salts  which  produce  hardness,  but  this  is  not  accurate 
quantitative  analysis.  It  should  be  ciearly  understood  that  the 
chemical  action  is  multiple  and  indefinite,  and  altogether  different 
from  that  which  usually  takes  place,  when  in  quantitative  analj'sis 
we  titrate  one  definite  compound  against  another.  All  that  can 
be  claimed  for  the  soap  process  is  that  it  indicates  the  amount  of 
soap-destroying  bodies  present  in  a  given  water,  but  fails  to  form 
a  measure  for  any  in  particular. 

The  following  compounds  produce  hardness: 

CaCOg,  MgCOg,  CO2  in  solution,  CaS04,  MgS04,  FeoOg,  and  other 
Peroxides,  zinc  salts,  Si02,  A\^  (OH)e,  chlorides,  nitrates,  phosphates, 
and  free  mineral  and  organic  acids. 

The  temporary  hardness,  which  is  got  rid  of  by  boiling,  is  fcr 


22  PRACTICAL  SANITARY  SCIENCE 

the  most  part  produced  by  CaCO^  and  MgCOg,  held  in  sokition  by 
COo.  After  these  come  small  quantities  of  CaS04  and  MgS04, 
which  are  also  thrown  out  immediately  C0.>  is  driven  off,  but  the 
great  bulk  of  these  sulphates  remains  in  solution.  Lasth',  in  a 
few  cases  minute  quantities  of  oxides  of  Fe,  silica,  and  alumina 
are  deposited.  Phosphate  of  Ca,  if  present  in  appreciable  quantity, 
may,  under  certain  conditions,  be  deposited  in  very  small  amounts. 
On  cooling  some  of  the  precipitated  MgC03,  and  to  a  less  degree 
CaCOg,  CaS04,  and  Ca3(P04).,  will  redissolve  and  go  to  form  per- 
manent hardness. 

MgCOg  destro^'S  nearly  50  per  cent,  more  soap  than  CaCOg,  but 
is  found  in  potable  waters  in  very  much  less  quantity. 

Estimation  of  Hardness. — Prepare  a  standard  solution  of 
calcium  chloride  in  the  following  manner:  Weigh  accuratel}^  0-2 
gramme  pure  calcite  (CaCOg),  and  dissolve  it  in  dilute  HCl,  taking 
care  to  keep  the  vessel  covered  so  as  to  avoid  loss  by  spirting.  Evap- 
orate this  solution  to  dr3mess  on  the  water-bath.  Add  water,  and 
again  evaporate  to  dryness,  and  repeat  these  processes  in  order  to 
remove  all  free  hydrochloric  acid.  Now  dissolve  the  residue  of  neutral 
CaClo  in  water  and  make  up  to  a  litre.  One  c.c.  =  the  equivalent 
of  0-2  milligramme  CaCOg.  In  other  words,  this  solution  possesses 
hardness  =  20  parts  per  100,000. 

Prepare  a  standard  soap  solution  by  dissolving  about  13  grammes 
of  Castile  soap  in  a  litre  of  equal  parts  methylated  spirit  and  water. 
Stand  in  a  cool  place  for  some  hours,  and  filter. 

The  titration  and  dilution  of  this  soap  solution  is  carried  out  as 
follows : 

Make  up  50  c.c.  of  the  calcium  chloride  solution  to  100  c.c.  with 
distilled  water  (10  parts  hardness  per  100,000),  and  place  in  a 
stoppered  bottle  of  250  c.c.  capacity.  Run  in  from  a  burette,  i  c.c. 
at  a  time,  the  soap  solution.  Close  the  bottle,  and  shake  vigorously 
for  a  short  period  until  a  lather  remains  on  the  surface  as  an  un- 
broken layer  for  five  minutes.  Towards  the  end  of  this  operation 
the  amount  of  soap  solution  added  should  be  lessened,  and  finally 
should  not  exceed  i  c.c.  As  the  end  is  reached,  the  sound  and  shock 
produced  by  shaking  becomes  much  more  gentle. 

The  student  should  carefully  prepare  a  number  of  similar  lathers 
by  shaking  100  c.c.  distilled  water  in  a  similar  bottle,  and  note 
exactly   the   amount    of    soap   solution   required.      This    quantity 


THE  CHEMICAL  EXAMINATION  OF   WATER  23 

will  be  found   to  be  about   i  c.c.  of  the   finished  standard  soap 
solution. 

In  the  present  case  the  quantity  of  soap  solution  used  should  be 
II  c.c.  (10  c.c.  to  precipitate  the  equivalent  of  10  milligrammes  of 
CaCOg,  and  i  c.c.  to  produce  the  lather).  Suppose,  however,  that 
9  c.c.  soap  solution  be  found  sufficient  to  produce  the  characteristic 
lather,  it  is  evident  that  the  solution  must  be  diluted  with  aqueous 
spirit  in  the  proportion  of  9  to  11.     Dilute,  therefore,  900  c.c,  or 

thereabouts,  of  the  original  litre  to  the  volume  ~ c.c,  and 

9 

keep  the  remainder  for  fortifying  the  standard,  as  in  time  it  loses 

strength,  especially  when,  on  keeping,  it  becomes  turbid.     Label 

the  solution  Standard  Soap  i  c.c.=  i  miUigramme  CaCOg. 

Should  the  soap  solution  prove  too  weak,  it  must  have  additional 
soap  added  and  be  put  through  the  same  process  of  standardization 
imtil  found  correct. 

A  standard  soap  solution  may  be  prepared  in  another  way: 
Dissolve  80  grammes  chemically  pure  oleic  acid  in  alcohol,  add  a 
few  drops  phenolphthalein  and  a  strong  solution  of  KOH  in  alcohol, 
until  the  oleic  acid  is  neutralized  and  saponification  therefore  com- 
plete (the  liquid  retains  the  faintest  purple  colour) ;  then  titrate  with 
the  calcium  chloride  solution,  and  dilute  to  standard  strength. 

The  following  is  an  example  of  the  determination  of  the  hardness 
of  a  sample  of  a  London  (New  River)  water: 

Take  100  c.c.  of  the  water  in  a  200-c.c.  stoppered  bottle.  Fill 
a  50-cc  burette  mounted  on  a  stand  with  standard  soap  solution 
(i  c.c.=  i  milhgramme  CaCOg).  Run  in  the  soap  solution  i  c.c 
at  a  time,  shaking  vigorously  after  each  addition,  until  a  permanent 
lather  remains  unbroken  for  five  minutes  when  the  bottle  is  laid  on 
its  side.  As  the  end  of  the  reaction  approaches,  the  hard  metallic 
sound  at  first  heard  on  shaking  gives  place  to  a  dull  thud,  the  froth 
which  previously  disappeared  almost  instantaneously  remains,  and 
adheres  in  specks  to  the  sides  of  the  bottle. 

Twenty-one  c.c  of  standard  soap  solution  were  required  in  this 
case  to  complete  the  titration.  Subtracting  i  c.c.  used  in  producing 
the  lather,  we  find  that  20  c.c  were  precipitated  by  the  100  c.c  of 
water. 

But  each  c.c.=  i  milligramme  CaCOg ; 
.-.  20  c.c.=  20  milligrammes  CaCOg, 


24  PRACTICAL  SANITARY  SCIENCE 

and  100  c.c.  of  this,  water  contains  20  milligrammes  of  soap-precipi- 
tating substances,  or  a  '  total '  hardness  equal  to  20  parts  per 
100,000.  In  waters  containing  magnesium  salts  the  lather  is  slowly 
produced,  and  of  a  dirty,  granular  appearance,  very  unlike  the 
light  frothy  condition  seen  in  hard  waters  destitute  of  Mg  salts. 

To  obtain  the  '  permanent '  hardness  in  the  above  example,  place 
100  c.c.  in  a  small  beaker  on  a  porcelain  ring  over  a  Bunsen  flame, 
and  boil  for  fifteen  minutes,  or  till  one-third  of  the  volume  has 
evaporated.  Filter  into  a  clean  100-c.c.  flask,  and  make  up  to  the 
mark  with  distilled  water.  Transfer  to  the  stoppered  bottle  and 
determine  the  hardness  as  above:  this  is  '  permanent  hardness.' 

13-5  c.c.  of  the  soap  solution  were  required  to  lather  the  100  c.c. 
of  water  prepared  as  described. 

13-5  c.c  — I  c.c.=  12-5  c.c, 

or  12-5  parts  permanent  hardness  per  100,000. 

The  'temporary  hardness '  =  difference  between  'total'  and 
'  permanent  '  hardness. 

20— 12-5  =7*5  parts  temporary  hardness  per  100,000. 

Hard  waters,  whilst  palatable,  cause  waste  of  soaps,  and  fail 
somewhat  in  cooking  vegetables,  meats,  etc.,  and  in  making  infu- 
sions of  tea  and  coffee.  They  are  unsuitable  for  boilers,  in  that  a 
deposit  forms  on  the  interiors  which  by  reason  of  its  low  conductivity 
of  heat  wastes  fuel,  and  from  its  divergent  coefficient  of  expansion 
may  lead  to  explosions. 

This  deposit  or  crust  will  consist  of  bodies  representing  both 
temporary  and  permanent  hardness.  Carbonates  of  Ca  and  Mg 
will  fall  out  first,  and  be  followed  by  their  sulphates,  together  with 
salts  of  iron,  silica,  and  alumina. 

In  this  country  the  hardest  waters  arise  from  the  chalk,  dolomite, 
and  new  red  sandstone  strata,  carbonates  of  Ca  and  Mg  forming  by 
far  the  largest  proportions  of  soap-destroying  compounds. 

Where  the  hardness  exceeds  20  parts  per  100,000,  it  is  well  in 
performing  the  estimation  to  dilute  the  sample  with  an  equal  bulk 
of  distilled  water.  The  total  hardness  of  a  potable  water  should 
not  exceed  25  to  30  parts  per  100,000.  Waters  whose  hardness 
falls  below  10  parts  are  considered  soft,  whilst  those  containing 
20  to  30  parts  are  hard,  and  upwards  of  30  parts  very  liard. 


THE  CHEMICAL  EXAMINATION  OF  WATER  25 

Clark's  scale  of  degrees  represents  hardness  as  grains  per  gallon 
(parts  per  70,000). 

It  is  universally  agreed  that  a  good  water  should  contain  less 
than  10  parts  per  100,000  of  permanent  hardness,  and  of  this  little 
should  be  due  to  magnesium  salts. 

Temporary  hardness  can  be  easily  got  rid  of;  not  so  permanent. 

In  Clark's  process,  as  noted  above,  slaked  lime  is  used  for  softe ning 
— in  other  words,  for  combining  with  the  COg  in  ^:olution,  thereby 
causing  insoluble  carbonates  to  separate  out  which  were  previously 
held  in  solution  by  the  CO^.  Care  should  be  taken  that  no  excee;s  of 
lime  is  added. 

CaCOg,   H2O,   C02  +  Ca(OH)2=2CaC03  +  2H20. 

Softening  of  permanent  hardness  may  be  effected  by  the  use  of 

NagCOg : 

CaS04  +  NagCOg  =  Na2S04  +  CaCOg. 

Clark's  method  does  not  yield  accurate  results  if  a  large  quantity 
of  Mg  salts  is  present.  These  salts  do  not  materially  affect  the  pro- 
cess now  to  be  described. 

Estimation  of  Hardness  by  Standard  Acid. — Determine 
first  the  temporary  hardness  by  titrating  the  calcium  and  magnesium 
salts  which  form  it  with  ~j^  H2SO4,  using  methyl  orange  (the  sodium 
salt  of  a  colour  acid  which  is  not  interfered  with  by  CO2)  as  indi- 
cator. 

Add  to  I  litre  of  the  water,  or  less  if  it  be  very  hard,  4  or  5  drops 
of  methjd  orange  solution,  and  run  in  —^  H2SO4  from  a  burette  until 
the  colour  changes  pink.  Calculate  the  weight  of  CaCOg  from  the 
number  of  c.c.  of  acid  used  and  convert  this  into  parts  per  100,000. 
Example. — 500  c.c.  water  required  9  c.c.  decinormal  sulphuric 
acid. 

I  c.c.  Y^  H2S04=  I  c.c.  ^  CaC03=  0-005  gramme  CaCOg; 
.'.  500  c.c.  water  =  0-005  x  9  grammes  CaCOg; 
.•.  100  c.c.  water=  o-ooi  X  9  ,, 

=  0-009  " 

^  =9  milligrammes  CaCOg. 

Hence  the  temporary  hardness  in  terms  of  CaCOg  =9  parts 
per  100,000. 

Permanent  Hardness. — To  250  c.c.  water  add  excess  -^  NaaCOg, 
say,  50  c.c,  and  boil  for  half  an  hour.     Should  Mg  salts  be  present, 


26  PRACTICAL  SAXITARY  SCIENCE 

evaporate  to  dryness  and  extract  the  residue  with  water.  Filter. 
Wash  the  precipitate  with  boiled  distilled  water.  Cool,  and  make 
up  the  filtrate  to  250  c.c.  Titrate,  say,  one-fifth  of  this  with 
■^^  H2SO4,  using  methyl  orange  as  indicator.  Calculate  from  the 
number  of  c.c.  acid  used  the  weight  of  NaoCOg  engaged  in  precipi- 
tating the  salts  forming  hardness,  and  from  this  the  permanent 
hardness  in  terms  of  CaCOg,  in  parts  per  100,000. 

Example. — 50  c.c.  taken  from  the  250  c.c.  cold  filtrate  required 
%-^  c.c.  ^^  H2SO4  for  neutralization. 

250  c.c.  require  %'d>  x  5  =  44  c.c.  J^,  H^SOj. 
50-44=  6  c.c.  yN.  NaaCOg  used 

=  6  c.c.  yN_  CaCOg 

=  0-005  ><  6  grammes  CaCOg  in  250  c.c.  water 

0-030 
=  — ^  ,,  ,,  100  c.c. 

2-5 
=  0-012 
or  12  parts  per  100,000. 
Temporary  hardness,  g. 
Permanent  hardness,  12. 
Total  hardness,  21. 

Water  containing  Na2C03  is  alkaline  in  reaction  and  contains  no 
permanent  hardness.  Since  boiling  fails  to  interfere  with  NagCOg, 
this  salt  can  be  estimated  in  the  filtrate  from  the  carbonates  of  Ca 
and  I\Ig  precipitated  by  boiling  in  the  above  process,  for  the  deter- 
mination of  permanent  hardness.  The  number  of  c.c.  -^  H2SO4 
used  X  0-0053=  weight  of  Na^COg. 

Rain  water  is  the  softest  of  all  natural  waters,  and  hardness  in- 
creases in  the  following  order:  Upland  surface  water,  river  water, 
spring  water,  deep-well  water,  shallow-well  water. 

Calcium  salts  react  quickly  in  the  double  decomposition  with 
soaps;  magnesium  salts  react  more  slowly.  Hence,  w-here  mag- 
nesium salts  are  present  in  quantity,  a  more  prolonged  shaking  is 
necessary  in  producing  the  characteristic  lather. 

Where  it  is  desirable  to  estimate  the  quantity  of  Mg  present  in  a 
sample,  the  ordinary  methods  of  quantitative  analysis  must  be 
employed. 

In  using  the  soap  test,  hard  waters  should  be  diluted  so  that  not 
more  than  16  c.c.  of  the  standard  soap  solution  is  required  to  complete 
the  reaction. 


THE  CHEMICAL  EXAMINATION  OF  WATER  27 


Solid  Residue. 

The  total  solids  in  waters  vary  greatly  in  extent,  ranging  from 
2  to  3  parts  in  rain  water  to  over  3,000  parts  in  sea  water  per  100, oco. 
From  the  purely  health  point  of  view,  perhaps  little  information 
will  be  derived  from  an  estimation  of  the  total  solids.  Occasions, 
however,  arise  in  which  it  may  be  desirable  to  estimate  the  total 
sohds,  and  also  the  quantities  of  certain  constituents,  such  as  Ca 
and  Mg  salts.  Where  these  latter  exist  in  large  quantity  in  the 
form  of  sulphates,  it  is  found  that  the  waters  are  unfit  for  drinking, 
from  their  action  on  the  alimentary  tract.  The  incineration  of 
the  dry  residue  affords  a  check  on  some  of  the  other  portions  of 
the  analysis  dealing  with  organic  matter.  On  the  whole,  any  useful 
information  that  can  be  obtained  will,  for  the  most  part,  centre 
round  the  quantities  of  Ca  and  Mg  salts  present,  especially  the 
sulphates. 

Chalk  waters  contain  little  sulphates;  hmestone  waters  hold 
chiefly  CaS04,  at  times  to  the  extent  of  15  to  20  parts  per  100,000; 
magnesium  limestone  (dolomite)  generally  contains  much  less 
CaS04  and  considerable  MgS04.  Sulphates  in  water  are  chiefly 
derived  from  strata;  a  very  small  amount  is  due  to  the  oxidation 
of  S  in  organic  matter;  a  small  quantity  in  the  rain  water  of  large 
towns  has  its  origin  in  the  solution  of  the  oxides  of  S  found  in  the 
atmosphere;  whilst  in  exceptional  cases  an  appreciable  portion  is 
due  to  the  oxidation  of  metallic  sulphides. 

Phosphates  in  marked  quantities  indicate  organic  pollution, 
especially  urine.  The  phosphates  of  the  alkalies  are  those  chiefl}^ 
found  in  water.  But,  in  that  certain  geological  beds  and  organic 
matter  of  purely  vegetable  origin  contain  phosphates,  no  very 
direct  information  is  obtained  from  their  estimation,  and  it  is 
usually  unnecessary  to  go  beyond  a  qualitative  examination. 

In  a  few  instances  silica  may  require  to  be  estimated:  this  com- 
pound lessens  the  plumbo-solvency  of  water. 

In  clear  waters  the  solids  are  all  in  solution;  in  turbid  waters 
they  are  partly  in  solution  and  partly  in  suspension.  It  is  cus- 
tomary to  estimate  the  solids  in  solution,  but  as  this  requires 
complete  sedimentation  it  may  be  advisable  in  cases  where  time 
is  limited  to  perform  the  estimation  on  the  sample  after  thoroughly 


28  PRACTICAL  SAXITARY  SCIENCE 

shaking.  The  method  adopted,  however,  should  be  stated  on  the 
report. 

Measure  out  loo  c.c.  of  the  water,  and  place  in  a  clean  platinum 
basin  on  a  water-bath,  25  c.c.  at  a  time,  as  evaporation  proceeds. 
When  dr}',  transfer  the  basin,  after  carefully  wiping  the  outside, 
to  an  air-bath  at  ^y°  C.  for  half  an  hour.  Remove  to  a  desiccator 
for  ten  minutes,  and  weigh.  By  drying  at  this  low  temperature 
no  water  of  crystallization  is  lost,  and  no  decomposition  takes  place. 
Further  drying  should  be  effected,  if  necessary,  until  a  constant 
weight  is  obtained.  This  weight,  less  that  of  the  dish,  represents 
the  total  solids. 

\\"\i\\  platinum-tipped  tongs  hold  the  dish  over  a  Bunsen  flame 
until  thorough  incineration  is  effected.  After  cooling  in  the  desic- 
cator, weigh  again  to  obtain  the  non-volatile  solids.  The  difference 
between  this  last  and  the  previous  weight  represents  the  volatile 
solids.  The  degree  of  charring  (organic  matter)  which  occurs  during 
incineration  should  be  noted;  also  the  smell  — odour  of  burnt 
sugar  indicates  vegetable  matter,  burnt  horn  animal  substance. 

Ca. — Where  it  is  deemed  necessary  to  estimate  the  quantity  of  Ca 
salts,  Mg  salts,  or  both,  500  c.c.  of  the  sample  should  be  evaporated 
down  to  200  c.c,  and  the  Ca  removed  by  precipitation  with 
(NH4)H0,  NH^Cl,  and  [^li^)X.^i.  The  precipitate  of  CaC204, 
when  thoroughly  washed,  dried,  ignited,  and  weighed,  represents 
the  Ca  as  CaCOg,  56  per  cent,  of  which  is  Ca.  The  weight  of  the 
crucible  and  ash  of  filter-paper  must  be  accurately  known  and 
accounted  for.  It  is  well  to  let  the  beaker  or  other  vessel  containing 
the  mixture  of  precipitate  and  fluid  stand  for  some  hours  in  a  warm 
place,  b}^  which  filtration  is  rendered  much  more  easy  and  thorough. 
The  student  may  be  reminded  that  the  addition  of  NH4CI  holds 
Mg  salts  in  solution. 

Mg*. — Concentrate  the  filtrate  down  to  one-fifth  its  bulk  or  less. 
Add  shght  excess  of  sodium  phosphate,  and  stand  aside  in  a  warm 
place  for  some  hours.  Filter,  wash  the  precipitate  well  with  dilute 
(NH4)H0,  dry,  ignite,  and  weigh  as  MgoP207  (magnesium  pyro- 
phosphate).    The  Mg  forms  t^V  of  this  weight. 

Phosphates. — It  is  rarely  necessary  to  estimate  phosphates. 
Where,  however,  required,  proceed  as  follows : 

Evaporate  200  c.c.  of  the  water  to  dryness.     Moisten  the  residue 


THE  CHEMICAL  EXAMINATION  OF  WATER  29 

with  a  few  drops  of  pure  HNO.5  and  evaporate  again  to  dryness, 
in  order  to  render  insoluble  any  silica  that  may  be  present.  Dis- 
solve in  dilute  HNO3  and  filter.  Add  ammonium  molybdate  in 
slight  excess;  keep,  if  possible,  in  a  warm  place  over  night,  and 
filter.  Wash  the  precipitate  well  with  hot  water,  and  dissolve  in 
ammonia.  Add  a  few  drops  NH4CI  and  shght  excess  of  MgClg, 
and  filter.  Wash  the  precipitate  thoroughly  with  dilute  am.monia. 
Dry,  ignite,  and  weigh  the  MgaPgO^.  The  phosphates  returned 
in  the  form  of  P2O5  will  be  represented  by  yy^  of  this  weight. 

It  is  hardly  necessary  to  say  that  a  qualitative  test  for  phosphates 
should  be  carefully  performed  before  entering  on  the  more  lengthy 
quantitative  estimation.  For  this  test  concentrate  by  evapora- 
tion a  quantity  of  the  water — say  200  c.c. — to  one-tenth  its  bulk. 
To  10  c.c.  in  a  test-tube  add  a  drop  or  two  of  HNO3,  i  or  2  c.c. 
solution  of  ammonium  molybdate,  and  heat  to  a  temperature 
somewhat  below  boiling,  for  several  minutes  if  necessary.  A  green- 
ish-3'ellow  coloration  indicates  traces  of  phosphates,  a  canary-yellow 
colour  an  appreciable  amount,  and  a  yellow  precipitate  larger 
quantities. 

Silica. — ^This  compound  generally  exists  in  water,  either  as 
soluble  silicates  of  the  alkalies,  or  as  insoluble  silicate  of  alumina. 
Evaporate  300  c.c.  of  the  water  to  dryness  after  acidulating  with 
HCl.  Treat  the  residue  with  strong  HCl,  and  transfer  by  washing 
to  a  filter  with  boiling  water.  Dry,  ignite,  and  repeat  the  fore- 
going treatment  with  acid  and  boihng  water  three  or  four  times. 
Finally  dry,  ignite,  and  weigh  as  SiOa- 

Sulphates  are  readily  detected  by  concentrating  to  about  one- 
tenth,  and  adding  to  the  warmed  sample  a  drop  of  HCl  and  a  few 
drops  of  BaCla  in  solution,  when  a  white  insoluble  precipitate  of 
BaS04  is  formed  and  rapidly  sinks  to  the  bottom  of  the  test-tube. 
The  insolubility  of  this  precipitate  should  always  be  tested  with 
sufficient  strong  nitric  acid. 

Estimation  of  Sulphates. — A  measured  quantity  of  the  water 
is  heated  to  boiling  in  a  beaker ;  a  few  drops  of  HCl  are  added,  and 
sufficient  hot  solution  of  BaClg  to  precipitate  the  whole  of  the 
sulphates  run  in.  Time  is  given  to  the  precipitate  to  settle,  and 
a  little  more  of  the  BaClg  allowed  to  fall  into  the  supernatant  clear 
solution.     If  no  turbidity  is  produced  the  reaction  is  complete; 


30  PRACTICAL  SANITARY  SCIEXCE 

but  if  even  the  slightest  turbidity  occur  more  BaClg  must  be  added, 
and  the  mixture  again  allowed  to  settle,  until  the  addition  of  a  drop 
of  BaCU  produces  no  turbidity.  The  white  precipitate  is  collected 
on  a  filter-paper,  the  weight  of  whose  ash  is  known,  well  dried, 
ignited  in  a  cmcible,  and  weighed  as  BaS04. 

The  SO4  is  returned  as  tr-yW  of  this  weight. 

Alkaline  phosphates,  sulphates,  and  chlorides  may  indicate 
animal  organic  matter,  especially  urine,  but  it  is  often  difficult  to 
attribute  to  these  salts  a  source  in  recent  pollution,  as  all  are  found 
in  strata  free  from  organic  matter.  Where  marked  excess  is  found, 
the  composition  of  the  geological  strata  accurately  known,  and 
where  frequent  analysis  of  pure  waters  from  the  same  strata  are 
made,  an  increase  of  any  or  all  may  be  attributed  to  organic  pollu- 
tion. But  it  should  be  remembered  that  slight  variation  in  amount 
of  these  salts  is  met  with  from  time  to  time  in  waters  arising  in 
certain  strata,  where  contamination  is  out  of  the  question. 

Nitrites,  nitrates,  and  poisonous  metals,  when  present,  will  be 
found  in  the  dry  residue  forming  the  total  solids.  The  metals  are 
most  easily  detected  in  this  residue. 

Poisonous  Metals. 

There  are  only  a  few  metals  whose  compounds  are  found  in 
water-supplies.  Lead  and  copper  are  the  chief;  occasionally  iron 
and  zinc  occur;  and  ver}-  rarely  chromium  and  tin. 

A  qualitative  examination  should  be  performed  in  all  cases  for 
each  of  these  metals;  and  where  a  possibility  of  other  metallic- 
compounds  derived  from  mines,  industrial  wastes,  etc.,  exists,  a 
further  careful  investigation  is  necessar}-. 

Lead. — Waters  possessing  an  acid  reaction,  such  as  those  derived 
from  peaty  moorlands,  in  which  organic  acids  (ulmic,  geic,  etc.) 
are  formed  by  certain  micro-organisms,  dissolve  lead.  The  primary 
action  of  water  on  lead  is  an  oxidation.  In  alkaline  and  strictly 
neutral  waters  the  coating  of  oxide  remains  intact,  but  in  acid 
waters  it  dissolves.  Hard  waters  containing  abundant  carbonates 
form  an  insoluble  ox^xarbonate ;  hence  hard  waters  lack  the 
property  of  dissolving  lead.  Houston  distinguishes  between  the 
solvent  action  of  acid  waters,  and  the  '  erosive  '  action  of  neutral 
waters  containing  dissolved  oxygen.     Acid  waters  should  be  cut 


THE  CHEMICAL  EXAMINATION  OF  WATER  31 

out  of  public  supplies,  if  they  cannot  be  passed  through  chalk, 
limestone,  etc.,  so  as  to  be  completely  neutralized.  Four  parts 
of  CaCOg  or  MgCOg  per  100,000  are  necessary  to  eliminate  plumbo- 
solvency. 

The  effects  of  acid  moorland  waters  on  lead  have  been  only  too 
clearly  seen  in  certain  districts  of  Yorkshire  and  Lancashire,  where 
the  inhabitants  have  suffered  from  anaemia,  constipation,  colic, 
wrist-drop,  depression,  gout,  renal  disease,  and  other  classical 
effects  of  lead-poisoning.  The  lead  is  dissolved  out  of  materials 
of  joints,  block-tin  pipes,  house  pipes,  cisterns,  etc. 

Whilst  carbonates  and  sulphates  in  water  diminish  pkimbo- 
solvency,  nitrates  favour  it,  as  lead  nitrate  is  the  most  soluble 
salt  of  the  metal.  A  rise  in  temperature  up  to  48°  to  50"  C.  increases 
plumbo-solvency. 

Compounds  of  lead  and  copper  in  acid  solution  are  precipitated 
as  sulphides  by  H2S.  [Pb,  it  should  be  remembered,  is  partially 
precipitated  from  strong  solutions  by  HCl  as  chloride.]  Copper  is 
not  precipitated  by  HCl  or  soluble  chlorides. 

The  precipitated  sulphides  of  Pb  and  Cu  are  insoluble  in  (NH4)2S 
and  KOH.  Strongly  acid  solutions  of  these  metals  are  not  pre- 
cipitated completely  until  suitably  diluted  with  water.  Lead 
sulphide  (PbS),  produced  by  adding  HgS  water,  or  bj^  passing  H2S 
gas,  is  black,  insoluble  in  KOH,  KCN,  and  (NH4)2S,  but  soluble 
in  boiling  dilute  HNO3;  it  is  changed  by  boihng  strong  HNO3  into 
white  insoluble  PbSO^. 

Solutions  of  lead  salts  on  addition  of  excess  of  dilute  H2SO4  give 
white  PbS04. 

K2Cr04  produces  a  yellow  precipitate  (PbCr04)  soluble  in  KOH, 
insoluble  in  acetic  acid. 

KI  precipitates  yellow  lead  iodide  (Pbl2),  more  insoluble  in  water 
than  the  chloride. 

Quantitative  Estimation.  —  Prepare  a  standard  solution  of 
Pb(C2H302)2,3H^O,  containing  O'oooi  gramme  Pb  per  c.c. 

The  molecular  weight  of  lead  acetate  is  379,  of  which  207  parts 

are  Pb.     Accordingly      -,  or  1-831,  grammes  of  the  salt  contam 

I  gramme   Pb.     Dissolve  therefore,  with  the  aid  of  a  little  free 
acetic  acid,  one-tenth  of  this  quantity — i.e.,  0-1831  in  a  litre  of 


32  PRACTICAL  SANITARY  SCIENCE 

water — and  each  c.c.  will  contain  ooooi  Pb.  To  loo  c.c.  of  the  water 
in  a  Nessler  glass  standing  on  a  white  tile  add  a  few  c.c.  dilute 
acetic  acid  and  sufficient  HoS  solution  to  precipitate  all  the  lead. 
To  100  c.c.  of  distilled  water  in  a  similar  Nessler  glass  add  the  same 
amounts  of  acetic  acid  and  HoS  solution,  and  run  in  from  a  burette 
or  pipette  the  standard  lead  acetate  solution  until  the  depth  of  tint 
in  the  two  Nesslers  is  exactly  the  same.  Perform  a  second  experi- 
ment, in  which  the  whole  volume  of  the  standard  lead  acetate 
solution  is  added  to  the  acidified  distilled  water  at  once,  and  then 
the  HoS  solution  added  and  well  mixed. 

The  weight  of  Pb  present  in  milligrammes  per  lOO  c.c.  (parts  per 
100,000)  =  0-1  milligramme  (o-oooi  gramme)  xthe  number  of  c.c. 
of  standard  lead  solution  used. 

It  may  be  necessary  to  dilute  the  water  sample,  in  which  case 
a  careful  record  of  the  amount  of  dilution  must  be  made,  and  taken 
into  account  in  calculating  the  result.  Or  it  may  be  necessary  to 
evaporate  500  c.c,  or  a  litre,  down  to  100  c.c,  and  to  use  this  for 
the  estimation.  Concentration  ma}'  be  necessary  also  in  the  quali- 
tative examination. 

Not  more  than  0-025  ps-^t  Pb  per  100,000  may  be  present  in 
water  without  producing  an  effect  when  the  water  is  drunk;  0-095 
per  100,000  has  proved  fatal,  and  0-050  is  dangerous.  In  a  word, 
all  drinking  water  should  be  free  from  lead,  as  its  poisoning  action 
is  increased  through  accumulation  in  the  body. 

Copper — Qualitative  Examination. — There  are  two  classes  of  copper 
salts — cupric  and  cuprous.  Cupric  salts  are  blue  or  bluish-green, 
and  when  freed  from  water  of  crystallization  become  pale  or  lose 
colour.  Cuprous  salts  are  usually  white  or  colourless;  they  yield 
red  CU2O  when  mixed  with  KOH,  and  white  CugL  when  mixed  with 
KI  solution.     CuO  is  black;  Cu.,0  red. 

A  little  dilute  NH4OH  added  to  solutions  of  copper  salts  produces 
a  greenish-blue  precipitate.  More  NH4OH  dissolves  the  precipitate, 
forming  an  intensely  blue  liquid. 

KOH  forms  a  pale  blue  precipitate,  which  when  heated  becomes 
black. 

H2SO4  produces  no  precipitate ;  difference  from  lead. 

K4Fe(CN)g  produces  a  reddish-brown  precipitate,  Cu2Fe(CN)f., 
insoluble  in  acetic  acid. 


THE  CHEMICAL  EXAMINATION  OF  WATER  33 

HgS  throws  down  a  brownish-black  precipitate  of  CuS  insoluble 
in  KOH,  (NH4)2S,  in  boiling  dilute  H2SO4;  soluble  in  boih'ng  HNO., 
and  in  KCN  solution. 

Quantitative  Estimation. — Prepare  "a  standard  solution  of  copper 
sulphate  containing  0-3929  gramme  CuS04,5H20  per  litre.  One  c.c. 
of  this  solution  =  0-000 1  gramme  Cu. 

Dilute  or  concentrate  the  water  if  necessary,  and  place  100  c.c. 
in  a  Nessler  glass  as  in  the  case  of  Pb.  Add  a  few  c.c.  decinormal 
acetic  acid  and  a  few  drops  K4Fe{CN)g  solution;  a  reddish-brown 
tint  is  produced.  Match  the  intensity  of  this  colour  in  a  similar 
Nessler  glass  by  mixing  the  necessary  volume  of  standard  copper 
solution  with  100  c.c.  distilled  water  and  the  same  quantities  of 
decinormal  acetic  acid  and  K4Fe(CN)g  as  were  added  to  the  glass 
containing  the  sample. 

The  number  of  c.c.  of  standard  copper  solution  x  o-i  gives  the 
weight  of  Cu  in  the  water  in  parts  per  100,000,  as  in  the  case  of  Pb. 

Not  more  than  o-i  part  per  100,000  Cu  is  permissible  in  potable 
water. 

Tin. — There  are  two  classes  of  tin  salts — stannous  and  stannic. 

1.  Pass  HgS  into  a  solution  of  stannous  salt  acidified  with  HCl:  a 
dark  brown  precipitate  soluble  in  KOH  and  yellow  ammonium  sul- 
phide forms  on  heating ;  reprecipitated  by  HCl  from  the  KOH  solu- 
tion as  brown  SnS,  and  from  the  ammonium  sulphide  solution  as 
yellow  SnSg.  [Note  SnS  is  insoluble  in  colourless  ammonium  sulphide.] 

2.  Add  HgClg  to  acidified  solution  of  a  stannous  salt:  a  white 
precipitate,  Idg^Cl^;  turns  grey  on  boiling  if  the  Sn  salt  is  in  excess 
through  formation  of  metallic  mercury  and  stannic  chloride — 
Hg2C1.2  +  SnCl.2  =  Hga  +  SnCl4. 

3.  Add  to  the  acidified  stannous  salt  a  drop  of  Br-water  and  a 
little  AuClg!  purple  precipitate.     '  Purple  of  Cassius.' 

Stannic  salts  in  acidified  solution : 

1.  HjS:  yellow  precipitate  of  SnS.2,  soluble  in  both  yellow  and 
colourless  ammonium  sulphide;  soluble  in  KOH  on  heating;  re- 
precipitated  b}^  HCl  as  yellow  SnSg  from  both  solutions. 

2.  HgClg:  no  precipitate. 

3.  AuClg :  no  precipitate. 

Quantitative  Estimation  of  Tin  [Stannous  or  Stannic).- — In  a 
measured  quantity  of  water,  concentrated  if  necessary  to  a  small 

3 


34 


PRACTICAL  SANITARY  SCIENCE 


bulk,  precipitate  the  Sn  as  sulphide.  Stand  in  a  warm  place  till  the 
smell  of  H.,S  has  nearly-  disappeared.  Filter.  Wash  well.  Dry. 
Ignite  in  the  air  into  SnO.,.  Weigh,  and  calculate  the  Sn.  [Inciner- 
ate the  filter-paper  apart  from  the  precipitate,  and  add  tlie  ash  to 
the  crucible  containing  the  SnOo-] 

No  tin  should  be  present  in  drinking  water. 

Iron. — Ferruginous  waters  are  found  in  mountain  limestone, 
chalk,  Bagshot  sands,  and  greensands.  They  are  generally  opal- 
escent, and  slightly  3'ellow  in  colour.  The  metal  occurs  as  a 
bicarbonate  which  is  readily  converted  into  an  insoluble  carbonate, 
and  also  oxidized  into  the  w^ell-known  '  rust  ' — hydrated  ferric 
oxide,  FcaO^,  H-iO.  Ferrous  salts  decompose  nitrates,  absorbing 
0  and  producing  nitrites,  which  in  turn  are  further  reduced  to 
XH3.  This  reducing  action  accounts  for  the  free  NH3  often  found 
in  pure  waters  derived  from  the  greensands  and  other  strata. 

Chalybeate  waters  may  be  quite  clear  when  drawn,  but  as 
oxidation  of  the  Fe  proceeds  they  become  turbid  and  more  or  less 
brown.  The  insoluble  and  highly  oxidized  particles  dissolve  on 
the  addition  of  a  little  dilute  acid.  Such  turbidity  may  have  its 
origin  in  iron  pipes,  cisterns,  etc.,  in  addition  to  strata. 

Two  classes  of  iron  salts  exist :  ferrous,  in  which  Fe  is  divalent,  and 
ferric,  in  which  it  is  trivalent.  They  may  be  readily  distinguished 
b}'  the  three  reagents,  potassium  ferrocyanide,  K4Fe(CN)g,  potassium 
ferricyanide,  K3Fe(CN)fi  (a  solution  always  being  made  from  the  crys- 
tals immediately  before  use),  and  potassium  sulpho-cyanide,  KCNS. 


Reagent. 

Ferrous  Compound. 

Ferric  Compound. 

K4Fe(CN)6     - 

K3Fe(CN)6     - 
KCNS    - 

Light  blue  precipitate,  be- 
coming dark  blue  on  oxi- 
dation by  the  air,  HNO3, 
or  Br. 

Dark       blue       precipitate; 
Turnbull's  blue  insoluble 
in  HCl. 

No   red    colour. 

Dark    Prussian    blue,    in- 
soluble   in    HCl;    turned 
brown  by  KOH. 

No  precipitate. 

Blood-red   colour    (no   ])re- 
cipitate).        Colour      de- 
stroyed   by    dropping    a 
few  drops  into  a  solution 
of  HgClg. 

THE  CHEMICAL  EXAMINATION  OF  WATER  35 

Sulphuretted  hydrogen  passed  through  a  solution  of  a  ferric  salt 
reduces  it  to  the  ferrous  state,  with  deposition  of  S.  H^S  gives  no 
precipitate  with  a  ferrous  salt  in  acid  solution. 

(NH4)2S  precipitates  from  a  ferrous  salt  black  ferrous  sulphide. 
This  reagent  reduces  a  ferric  salt  to  the  ferrous  state,  and  then 
precipitates  ferrous  sulphide  with  S. 

Except  in  connection  with  greensands,  ferrous  iron  is  rarely,  met 
with  in  water  work,  ferric  salts  alone  being  found. 

(NHJaOH  produces  with  ferric  salts  a  reddish-brown,  flocculent 
precipitant,  FealOH)^,  insoluble  in  KOH,  soluble  in  HCl. 

(NH4)2S  precipitates  black  FeS  soluble  in  HCl,  insoluble  in  KOH. 

These  tests  with  the  above  reactions,  produced  by  K4Fe(CN)g  and 
KCNS  are  sufficient  to  identify  ferric  compounds  in  water. 

Quantitative  Estimation. — If  the  quantity  of  iron  is  small,  it  may 
be  estimated  colorimetrically  like  lead  and  copper,  in  which  case 
prepare  a  standard  solution  of  iron  alum,  Fe(NH4)(S04)2.i2H20, 
by  dissolving  o-86i  gramme  in  a  litre  of  distilled  water.  This  solu- 
tion contains  o-oooi  gramme  Fe  per  c.c.  If  necessary,  evaporate 
half  a  litre  of  the  water  to  100  c.c.  Place  this  in  a  Nessler  glass^ 
and  add  i  c.c.  of  dilute  K4Fe(CN)g  solution.  Match  the  colour  of 
the  liquid  in  this  glass  by  adding  to  100  c.c.  distilled  water  in  a 
similar  Nessler  the  same  amount  of  K4Fe(CN)g  and  the  requisite 
quantity  of  the  standard  iron  solution.  It  is  well  to  add  a  drop  or 
two  of  nitric  acid  free  from  iron  to  each  of  the  Nesslers. 

If  the  quantity  of  iron  is  too  great  for  colorimetric  estimation, 
acidify  a  litre  of  the  water  with  HCl,  and  evaporate  to  dryness. 
Complete  the  drying  in  the  air-bath  at  150°  C.  Moisten  with  HCl, 
add  water,  and  heat.  Filter  off  any  insoluble  silica  (which  may  be 
washed,  ignited,  and  weighed).  To  the  filtrate  add  a  few  drops 
pure  HNO3,  and  boil.  Then  add  a  little  (NH4)C1  solution  and  a 
shght  excess  of  NH4OH,  and  allow  the  precipitate  of  ferric  hydroxide 
to  settle.     Filter  this  off;  ignite  and  weigh  as  Fe^Og. 

[Should  it  be  necessary  to  estimate  Ca,  which  is  now  contained 
in  the  filtrate,  add  excess  of  ammonium  oxalate,  allow  to  settle, 
filter  off,  and  ignite  the  calcium  oxalate.     Weigh  as  CaO.] 

Not  more  than  o-i  part  Fe  per  100,000  should  be  present  in  a 
domestic  water.  A  distinct  chalybeate  taste  is  produced  by  0*3 
part  per  100,000. 


36  PRACTICAL  SANITARY  SCIENCE 

Chromium. — Evaporate  a  litre  of  the  water  to  be  tested  to 
dryness,  and  fuse  the  ash  with  solid  potassium  nitrate  and  sodium 
carbonate  to  produce  yellow  KoCr04,  which,  in  neutral  solution, 
produces  a  red  precipitate  with  AgNOg  (soluble  in  ammonia  and 
dilute  nitric  acid),  and  in. solution  in  acetic  acid  gives  a  yellow 
precipitate  with  lead  acetate  insoluble  in  dilute  acetic  acid.  A  few 
c.c.  of  a  largely  concentrated  sample  may  be  dropped  on  a  thin  layer 
of  ether  which  has  been  floated  on  a  dilute  solution  of  H2O2  acidi- 
fied with  H2SO4.  Upon  slight  agitation  the  blue  colour  which 
forms  in  the  lower  solution  passes  to  the  ether. 

In  chromates  (yellow  or  red  in  colour)  Cr  exists  in  combination 
with  oxygen,  acting  as  an  acid  radicle.  Cr  also  forms  a  set  of  salts 
in  which  it  acts  as  a  metallic  radicle.  These  are  green  or  violet  in 
colour,  but  pass  through  oxidation  into  chromates. 

Conversely,  chromates  pass  by  reduction  into  green  chromic 
compounds.  Acidify  a  chromate  with  HCl,  add  Zn,  and  warm; 
the  yellow  chromate  passes  into  a  green  chromic  salt. 

(NHJOH  and  KOH  in  small  quantity  produce  a  pale  bluish- 
green  or  purple  precipitate  of  Cr2(0H),j,  more  or  less  soluble  in  excess 
of  the  precipitant. 

Quantitative  Estimation. — A  chromate  is  first  transformed  by  a 
reducing  agent  into  a  chromic  salt.  A  solution  of  the  chromic  salt 
is  then  precipitated  by  NH4OH  in  presence  of  NH4CI,  and  the 
resulting  hydrate  converted  by  ignition  into  CraOg,  and  weighed. 
From  the  weight  of  CroOg  the  amount  of  Cr  is  calculated. 

No  chromium  should  be  present  in  a  drinking  water. 

Zinc. — Concentrate  the  water. 

(NH4)2S  produces  a  white,  flocculent,  gelatinous  precipitate, 
which  often  appears  yellow  owing  to  excess  of  yellow  ammonium 
poh'sulphide,  (NH4)2Sa.  This  reaction  is  characteristic,  as  zinc 
sulphide  is  the  only  white  sulphide  capable  of  being  precipitated. 
Zn  is  only  partly  precipitated  from  neutral  solution  by  HjS,  but  by 
adding  sufficient  NaOH,  NH4OH,  or  sodium  acetate,  the  whole  of 
the  metal  may  be  precipitated  by  this  reagent. 

Solution  of  NH4OH  gives  a  white  precipitate  of  Zn,  (0H)2,  readily 
soluble  in  excess  of  ammonia. 

K4Fe(CN)g  produces  a  white  gelatinous  precipitate  of  zinc  ferro- 
cyanide. 


THE  CHEMICAL  EXAMINATION  OF  WATER  37 

Quantitative  Estimation  of  Zn. — Prepare  a  standard  solution  of 
ZnS04,7H20.  In  287  parts  of  this  salt  there  are  65  of  Zn,  or  in 
4-4  parts  I  of  Zn.  Dissolve  4-4  grammes  of  the  crystals  in  a  htre 
of  water  (each  c.c.  =  o-ooi  gramme  Zn).  Use  this  standard  solution 
volumetrically,  as  in  the  case  of  Fe,  precipitating  the  Zn  with 
K4Fe(CN)p.  Avoid  much  excess  of  the  ferrocyanide.  This  may  be 
effected  by  placing  a  drop  of  the  mixture  on  a  white  tile  in  contact 
with  a  drop  of  a  saturated  solution  of  uranium  acetate,  when  a 
brown  colour  appears  immediately  free  ferrocyanide  is  present. 

Gravimetric  Estimation. — Heat  a  measured  quantity  of  the  con- 
centrated water  to  boiling,  and  add  slight  excess  of  a  solution  of 
NagCOg.  Boil  again,  and  allow  the  precipitate  to  settle.  Wash 
several  times  by  decantation  with  boiling  water;  transfer  the  pre- 
cipitate to  a  filter,  and  finish  the  washing  thereon.  When  finished 
the  wash-water  shows  no  alkalinity  to  litmus  and  gives  no  precipi- 
tate with  BaClg. 

Dry  the  precipitate,  and  carefully  transfer  it  to  a  porcelain  cruci- 
ble. Heat  to  redness.  Wet  the  filter-paper  with  strong  ammonium 
nitrate  solution,  and  dry  it;  incinerate  it  in  the  flame  in  a  coil  of 
platinum  wire,  and  let  the  ashes  fall  into  the  crucible.  The  flame 
should  not  enter  the  interior  of  the  crucible  during  ignition,  lest 
reduction  of  the  ZnO  take  place.  Cool  and  weigh.  Calculate  Zn 
from  ZnO. 

Carbonate  of  Zn,  ZnCOg,  is  found  in  certain  mineral  waters  in 
quantities  varying  from  q-ooi  to  0-005  parts  per  100,000.  As 
much  as  10  parts  per  100,000  ZnS04  have  been  detected  in  such 
waters.  Zinc  may  be  introduced  by  galvanized  iron  tanks  or  pipes. 
It  should  not  be  found  in  a  drinking  water. 


CHAPTER  IV 

ORGANIC  MATTER  IN  WATER 

As  vegetable  organic  matter  has  little  significance  from  the  sanitary 
point  of  view,  attention  is  almost  entirely  directed  to  animal  matter 
in  the  form  of  sewage.  It  is  not  proved  that  animal  organic  matter 
per  se  in  the  quantities  found  even  in  dilute  sewage  is  hurtful  to 
health;  its  importance  lies  rather  in  the  fact  that  pathogenic 
microbes,  especially  those  of  intestinal  origin,  accompany'  it. 
Wherever,  then,  faecal  matters  in  quantity  large  or  small  are  met 
with  danger  exists. 

The  complex  remains  of  dead  animals  and  plants  are  slowly 
changed  to  simple  inorganic  compounds  in  the  superficial  laj^ers  of 
the  soil  under  the  action  of  manifold  ferments,  the  products  of 
micro-organisms  in  association  with  favourable  quantities  of  heat, 
moisture,  and  oxygen.  The  sum  total  of  these  changes  is  spoken 
of  as  an  oxidation,  since  the  end  products  are  oxides  of  carbon, 
nitrogen,  etc. ;  but  there  is  no  doubt  that  as  in  the  case  of  the  various 
fermentations  which  take  place  in  the  alimentary  canal  of  animals, 
known  collectively  as  digestion,  reductions  frequently  alternate 
with  oxidations.  There  is  some  evidence  to  show  that  these  fer- 
ments, metabolic  products  of  aerobic  and  anaerobic  bacteria,  act 
along  certain  lines  which  are  intimately  correlated.  The  specific 
action  of  one  enzyme  furnishes  the  necessary  conditions  for  the 
opposed  functions  of  a  succeeding  enzyme. 

Whilst  an  accurate  qualitative  or  quantitative  estimation  of 
organic  matter  in  a  potable  water  is  impossible,  still  there  are 
certain  chemical  tests  of  value  in  directing  us  towards  the  source 
of  the  organic  matter,  which  source  maj'  ultimately  be  discovered 
by  other  means. 

A  rough  differentiation  of  animal  from  vegetable  matter  may  be 

38 


ORGANIC  MATTER  IN  WATER  39 

effected  by  a  consideration  of  the  ratio  of  '  organic  carbon  '  to 
'  organic  nitrogen,'  which  ratio  forms  the  basis  of  Frankland's 
well-known  method  of  estimating  organic  matter.  The  process  is 
only  suitable  for  experienced  chemists  and  laboratories  equipped 
with  apparatus  for  gas  analysis.  But  in  skilled  hands  it  is  simple 
and  direct.  A  measured  volume  of  water  is  carefully  evaporated 
to  dryness;  the  residue  is  introduced  into  a  hard  glass  tube  along 
with  some  oxide  of  copper,  and  the  tube  is  heated  in  a  furnace 
until  combustion  of  the  organic  matter  is  complete.  The  gaseous 
products  of  combustion — carbon  dioxide,  nitric  oxide,  and  nitrogen 
— are  severally  collected  and  weighed,  as  '  organic  carbon  '  and 
'  organic  nitrogen.'  If  in  surface  waters  the  proportion  of  organic 
carbon  to  organic  nitrogen  be  as  low  as  3:1'  the  organic  matter 
may  be  considered  as  of  animal  origin,  while  if  it  be  as  high  as 
8  :  I  it  is  chiefly  vegetable.  In  certain  fresh  peaty  waters  the  ratio 
of  C  :  N  has  been  found  as  high  as  12  :  i.  In  fresh  sewage  the 
proportion  of  C  :  N  may  be  2  :  i.  Frankland  held  that  the  smaller 
the  proportion  of  organic  carbon  and  organic  nitrogen  in  a  water, 
and  of  these  constituents  the  larger  the  proportion  of  C  :  N,  other 
things  being  equal,  the  better  is  the  quality  of  the  water. 

The  fermentation  of  dead  organic  matter,  known  as  '  putrefaction,' 
is  effected  by  many  types  of  micro-organisms. 

Dead  proteins  are  hydrolysed  to  proteoses;  these  to  peptones; 
peptones  to  amino-acids;  finally  amino-acids  are  split,  evolving 
ammonia. 

If  we  follow  this  ammonia  as  it  escapes,  say,  from,  a  dung-heap 
in  solution  into  the  soil,  we  shall  find  that  in  the  presence  of  the 
'  nitrous  '  organisms  nitrous  acid  is  formed,  which  in  contact  with 
the  bases  of  the  soil  rapidly  becomes  nitrites.  Later,  through  the 
activities  of  the  '  nitric  '  group  of  micro-organisms,  nitric  acid  is 
generated,  which  speedily  becomes  nitrates.  These  various  stages 
in  the  oxidation  or  purification  of  nitrogenous  matters  stand  out  as 
chemical  landmarks,  and  present  considerable  information  to  the 
water  analyst. 

As  carbohydrates  and  fats  are  much  less  complex  bodies  contain- 
ing C,  H,  and  0  only,  their  decomposition  and  oxidation  are  much 
more  simple:  carbon  is  burnt  to  COg,  and  H  to  HoO. 

These  changes  in  nitrogenous  matter  ma}^  be  studied  directly. 


40 


PRACTICAL  SANITARY  SCIENCE 


If,  for  example,  A  be  a  source  of  organic  pollution,  say  a  manure- 
heap,  on  the  surface  of  the  ground,  and  B,  C,  D,  and  E  wells  at 
increasing  distances  from  it,  analysis  will  show  that  the  water  in 
B  contains  abundance  of  NH., ;  nitrification  has  not  yet  taken  place. 
At  C  the  oxidation  processes  have  advanced  to  the  stage  of  nitrous 
acid;  this  water  will  contain  less  ammonia  and  some  nitrites.  The 
water  from  D  has  travelled  farther,  encountering  more  nitrifying 
organisms,  with  the  result  that  ammonia  has  disappeared,  and  nitrites 
and  nitrates  are  found.  At  E  purification  is  complete — the  whole 
of  the  N  is  oxidized  to  nitric  acid;  hence  this  water  contains  no 
NHg,  no  nitrites,  but  onh'  nitrates. 

The  opportunities  for  purification  offered  between  A  and  B  are  not 
sufficient  to  carry  the  oxidation  changes  beyond  the  stage  of  NH.,; 
whereas  the  journey  from  A  to  E  is  of  such  length  that  the  entire 

A  B  C  0  C 


Nitrite 

*""  Nitrate 

Nitrite  Nitrate 

Fig.  3. 

changes  have  been  completed.     At  intermediate  points  are  observed 
intermediate  stages  in  the  purification. 

From  the  consideration  of  a  single  instance  of  this  kind,  no  con- 
clusions as  to  the  distance  a  well  must  be  removed  from  a  source 
of  contamination  in  order  to  be  safe  can  be  drawn,  since  the  factors 
in  the  problem  of  safety  are  numerous  and  variable.  The  distance 
between  A  and  E,  if  the  water  in  E  is  to  be  completely  purified, 
would  require  to  be  much  greater  if  the  slope  from  A  to  E  be  con- 
siderable, or  E  would  need  to  be  much  deeper.  On  the  other 
hand,  if  the  slope  of  the  ground  water  descended  from  E  to  A,  it 
is  possible  that  the  water  of  B  may  be  free  from  all  organic  matter. 
The  porosity  of  the  soil,  conditions  of  heat  and  moisture  necessary 
to  vigorous  growth  of  purifying  organisms,  direction  of  slope  of 
ground  water,  geological  features  of  subsoil  and  underlying  strata, 
rainfall,  and  a  number  of  other  factors,  all  influence  this  question 
of  safe  distance  of  well  waters  from  foci  of  contamination.  Each 
case  must  be  worked  out  on  its  ow-n  merits;  and  here  the  chemical 


ORGANIC  MATTER  TN  WATER  41 

examination  renders  useful  service.  A  sample  of  water  from  E 
may  be  pure  to-day — that  is,  contain  no  organic  matter  as  such, 
no  NH3,  no  nitrites,  but  only  nitrates ;  to-morrow,  owing  to  increased 
rainfall,  whereby  more  organic  matter  than  usual  is  washed  into 
the  soil,  or  to  some  other  condition  by  which  the  powers  of  the  soil 
for  purification  are  lessened,  this  same  water  may  contain,  besides 
nitrates,  nitrites,  NH3,  and  even  undecomposed  organic  matter. 
It  should  ever  be  borne  in  mind  that  the  machinery  by  which 
organic  matter  is  purified  in  the  soil  is  liable  at  any  point  to  break 
down,  and  in  too  many  instances  although  just  sufficient  for  the 
work  is  near  breaking-point.  The  question,  therefore,  should  be, 
not  how  near  to  a  focus  of  contamination  may  it  be  safe  to  procure 
water,  but  rather  how  far  from  the  focus  is  it  possible  to  acquire 
it.  Chemical  analysis,  if  frequently  and  regularly  performed,  will, 
in  most  cases,  discover  such  breakdown  in  the  purification 
machinery,  although  a  single  analysis,  unaccompanied  by  further 
information  as  to  source  and  surroundings,  may  be  quite  useless. 
It  is  the  comparative  information  regarding  a  water  acquired  by 
systematic  and  repeated  analyses  that  is  of  value. 

The  student  should  note  that  the  nearer  the  nitrogenous  organic 
matter  of  domestic  sewage  stands  to  the  stage  of  raw  proteins 
the  worse,  as  it  is  in  this  stage  that  pathogenic  bacteria  are  found 
in  their  most  toxic  and  vigorous  condition;  and  that,  conversely, 
the  farther  from  this  stage  such  matter  stands  the  less  dangerous 
it  is.  When  organic  matter  reaches  the  stage  of  nitrates  no  patho- 
genic germs  will  live  in  it. 

From  the  standpoint  of  infection,  fresh  faecal  matter  and  urine 
are  the  most  dangerous  of  all  forms  of  organic  matter. 

It  is  not  possible  in  water  analysis  to  separate  and  estimate  raw 
proteins,  proteoses,  peptones,  and  amino-acids.  The  next  stage, 
that  of  NH3,  lends  itself  to  ready  estimation. 

When  this  '  free  and  saline '  ammonia,  as  it  is  called,  is  removed, 
the  remaining  organic  matter,  which  consists  of  the  nitrogenous 
complexes  constituting  the  antecedent  stages,  can  be  rapidly 
oxidized  by  the  aid  of  a  powerful  oxidizer  and  heat  (^\'anklyn's 
process)  into  ammonia,  and  estimated  as  '  albuminoid '  ammonia. 
This  figure,  inasmuch  as  it  measures  those  portions  of  the  nitrog- 
enous organic  matter  likely  to  contain  pathogenic  micro-organisms. 


42  PRACTICAL  SAXITARY  SCIEXCE 

is  obvioush'  the  most  important  determination  connected  \vith  this 
portion  of  tlie  subject. 

Estimation  of  'Free  and  Saline'  NRj. — Prepare  a  standard 
solution  of  (XHjjCl,  i  c.c.  of  which  =  o-oi  milhgramme  NH3. 

53-5  grammes  NH4CI  contain  17  grammes  NH3. 
3-14         ,,  ,,  ,,  I  gramme  NH3. 

Dissolve  3-14  dr}'  anhydrous  NHjCl  in  i  Htre  ammonia-free 
distilled  water.  One  c.c.  of  this  solution  =1  milligramme  NH3. 
This  is  too  strong.  Dihite  10  c.c.  of  it  to  a  litre;  i  c.c.  now=o-oi 
milligramme  XH3. 

The  process  depends  on  the  fact  that  when  the  water  is  distilled 
with  a  little  sodium  carbonate  all  the  ammonia  in  the  water,  free  or 
combined,  passes  over  in  the  first  portions  of  the  distillate,  and  may 
be  estimated  by  Nessler's  solution. 

Prepare  Nessler's  solution.  Dissolve  62'5  grammes  KI  in  about 
250  c.c.  distilled  water.  Set  aside  a  few  c.c.  of  this  solution.  Now 
add  to  the  larger  portion  saturated  mercuric  chloride  solution  till 
precipitated  mercuric  iodide  cea,ses  to  dissolve  on  stirring.  Add 
the  reserved  KI  so  as  to  redissolve  the  precipitate,  and  again  add 
cautiously  sufficient  mercuric  chloride  solution  to  produce  a  shght 
permanent  precipitate. 

Dissolve  150  grammes  KOH  in  about  300  c.c.  water;  cool;  add 
gradually  to  the  above  solution,  and  make  up  with  HoO  to  a  litre. 
A  brown  precipitate  settles  out  on  standing,  and  the  supernatant 
fluid  is  clear  and  of  a  pale  greenish-yellow  colour.  It  is  ready  for 
use  as  soon  as  it  is  perfect!}'  clear.  It  should  be  decanted  without 
stirring  up  the  sediment.  Keep  in  bottles  closed  with  well-fitting 
rubber  stoppers.  This  solution  is  rendered  sensitive  from  time  to 
time  by  the  addition  of  a  little  more  HgCU  solution ;  its  sensitiveness 
depends  on  its  being  saturated  with  HgCU. 

Sodium  Carbonate. — Heat  anhydrous  NaaCOg  to  redness,  taking 
care  not  to  fuse  it ;  transfer  to  a  mortar,  and  grind  to  a  fine  powder. 
Store  in  a  clean,  dry,  wide-mouthed,  stoppered  bottle. 

Ammonia-free  water  is  prepared  bj'  distilling  ordinary  water  in 
the  presence  of  NaaCOg  or  H.,S04,  and  rejecting  the  first  portions  of 
the  distillate  until  there  is  no  trace  of  colour  produced  on  Nesslerising 
50  c.c.  of  it. 


ORGANIC  MATTER  IN  WATER  43 

A  preliminary  test  may  be  made  in  order  to  ascertain  what 
quantity  of  the  water-sample  should  be  distilled  in  order  to  make 
an  exact  determination  of  the  ammonia.  Place  two  Nessler  glasses 
on  a  white  tile;  add  50  c.c.  of  the  sample  to  one,  and  50  c.c.  am- 
monia-free distilled  water  to  the  other.  To  the  ammonia-free 
water  add  0-5  c.c.  of  the  dilute  standard  NH4CI  solution.  To  both 
Nesslers  now  add  2  c.c.  Nessler's  reagent,  and  stir.  If  on  standing 
five  minutes  the  intensity  of  colour  in  both  cylinders  is  the  same, 
500  c.c.  of  the  water  may  be  used  for  distillation.  If  the  intensity 
of  the  colour  of  the  sample  is  much  greater,  dilution  is  necessary 
prior  to  distillation,  otherwise  the  quantity  of  ammonia  in  the  first 
50  c.c.  distillate  will  be  too  large  to  match. 

Arrange  a  distilhng-flask,  condenser,  and  Bunsen  burner.  Pour 
into  the  flask  500  c.c.  of  the  water  (or  water  sufficiently  diluted); 
add  some  prepared  sodium  carbonate,  and  if  the  water  is  acid  a 
little  more  than  usual  (the  least  acidity  fixes  NH3).  Receive  in 
Nessler  glasses  150  c.c.  distillate  in  three  lots  of  50  c.c.  each.  The 
boiling  should  be  briskly  effected;  it  is  generally  useful  to  place  a 
piece  of  pumice  in  the  flask  to  prevent  bumping.  As  each  Nessler 
glass  is  filled  it  should  be  Nesslerised  or  covered  until  Nesslerisation 
is  accomplished. 

Nesslerisation  is  one  of  a  number  of  colorimetric  methods  of 
volumetric  analysis  in  which  the  amount  of  a  substance  is  esti- 
mated by  adding  to  it  a  second  body  capable  of  forming  a  char- 
acteristic colour  with  it.  The  same  conditions  are  accurately 
fulfilled  in  a  similar  vessel,  using  distilled  water  and  such  quantity 
of  the  substance  sought,  in  standard  solution,  as  will  match  the 
colour  of  the  first  when  the  same  quantity  of  the  second  body  is 
added.  In  order  that  shght  differences  in  tint  may  be  appreciated 
and  matched,  it  is  necessary  to  work  with  dilute  solutions  of  the 
body  to  be  estimated  and  the  standard  reagent ;  hence  the  necessity 
at  times  of  diluting  the  water  under  examination. 

Having  collected  the  three  50  c.c.'s  of  distillate,  Nesslerise  each 
separately.  Stand  the  Nessler  glass  on  a  white  tile  in  a  good  north 
light,  and  by  its  side  place  a  second  Nessler  glass  of  similar  shape 
containing  distilled  ammonia-free  water,  and  that  quantity  of 
standard  solution  of  (NHJCl  deemed  necessary  to  match  the  first. 
Into  each  deliver  2  c.c.  of  Nessler's  reagent,  and  carefully  mix.     In 


44  PRACTICAL  SANITARY  SCIENCE 

a  few  minutes  the  yellow  colour  will  have  fully  developed,  and  its 
depth  can  be  gauged  by  looking  down  through  the  column.  Should 
there  be  some  discrepancy  in  the  tints,  rapidly  add  to  another 
Nessler  glass  containing  distilled  ammonia-free  water  a  little  more 
or  a  little  less  of  the  standard  solution,  as  the  case  may  be,  until 
an  exact  match  is  produced.  In  all  such  colorimetric  work  every 
condition  should  be  exactly  similar  in  the  two  cases — length  of 
time  reagents  are  in  contact,  order  in  which  reagents  are  added, 
shape  and  size  of  containing  vessels,  etc.  The  standard  solution 
of  XH4CI  must  be  added  to  the  second  Nessler  glass  before  the 
Nessler's  reagent,  as  this  occurred  in  the  Nessler  glass  containing 
the  distillate.  If  the  standard  solution  be  added  after  the  Nessler 
reagent  an  opacity  is  likely  to  form  which  prevents  to  some  degree 
an  exact  match  being  made.  Several  trials  may  be  necessary  before 
an  accurate  result  is  reached. 

The  second  and  third  50  c.c.  of  the  distillate  are  treated  in  the 
same  way,  and  the  sum  of  the  results  in  terms  of  c.c.  of  the  standard 
solution  noted. 

\\'anklyn  found  that  the  whole  of  the  free  and  sahne  NH3  was 
contained  in  150  c.c.  distillate,  and  that  the  first  50  c.c.  contained 
three-fourths  of  the  total. 

Nesslerise  the  second  distillate  first,  and  note  whether  more  then 
1-5  c.c.  of  the  standard  NH4CI  solution  is  required  to  match  it.  if 
so,  the  first  distillate  must  be  diluted  before  Nesslerisation,  other- 
wise the  colour  will  be  too  intense  to  be  accurately  matched. 

Example. 

First  Nessler  glass  matched  by  3-00  c.c.  XH4CI  (ic.c.  =  o-oi  milligramme  XH3) 
Second     ,,  ,,  ,,         ,,    0-75 

Third        ,,  ,,  ,,  ,,    0-25 

Total  XH3=4'Oo     ,,  ,,  ,,  ,, 

But  each  c.c.  standard  NH4Cl  =  o-oi  milligramme  NH3; 
.■ .  4  c.c.  =  0*04 
And  in  500  c.c.  of  the  water  under  examination  there  is  0*04  milligramme  NH3. 
In  100  c.c.  there  will  be  o-ooS  milligramme  XH3,  or,  since  100  c.c.  water  = 
100,000  milligrammes,  this  water  contains  free  and  saline  XH3  to  the  extent  of 
O'OoS  part  per  100,000. 

Estimation  of  'Albuminoid'  NH3.— \Miilst  the  Nesslerisation 
of  the  free  and  saline  NH3  is  going  on,  50  c.c.  of  alkaline  potassium 
permanganate  (composed   of  200  grammes  KOH,  8  grammes  per- 


ORGANIC  MATTER  IN   WATER  45 

manganate,  a  litre  of  water)  should  be  boiled,  so  as  to  expel  any 
ammonia  that  it  may  contain,  and  to  heat  the  liquid  in  order  to 
prevent  cracking  the  retort  when  pouring  it  in.  Ihis  is  a  strongly 
oxidizing  reagent,  and  rapidly  converts  undecomposed  organic 
matter  into  NH3.  By  this  moist  combustion  process  a  degree  of 
oxidation  is  effected  in  the  course  of  half  an  hour  or  so  in  the 
laboratory  that  would  require  weeks  or  months  by  the  natural 
processes  outside. 

When  the  alkaUne  permanganate  is  ready,  the  cork  of  the  retort 
is  removed  and  the  hot  solution  poured  in. 

This  portion  of  the  distillation  should  be  carried  out  more  slowly, 
as  organic  matter  is  slowly  decomposed,  and  the  distillate  should 
be  collected  as  long  as  any  NH3  comes  over.  No  relation  exists 
between  the  number  of  the  Nessler  glasses  collected  and  the  total 
NH3,  as  in  the  case  of  the  free  and  saUne  portion.  Moreover,  the 
second  Nessler  may  contain  as  much  NH3  at  times  as  the  first. 

The  student  should  fit  up  his  apparatus  himself,  and  see  that 
all  connections  are  water-tight  and  gas-tight,  as  the  case  may  be. 
Corks  should  be  carefully  bored  and  made  to  fit  flasks  and  con- 
denser tubes,  and  indiarubber  corks  are  preferable  to  wood.  The 
distilling-flask  should  be  thoroughly  cleansed  with  weak  acid  and 
rinsed  out  with  distilled  water  until  all  traces  of  acid  have  dis- 
appeared. It  is  well  to  distil  some  pure  ammonia-free  water 
through  the  condenser  in  order  to  get  rid  of  any  traces  of  NH3 
that  it  may  contain  before  starting  the  distillation  of  a  sample.  A 
large  and  constant  stream  of  water  running  through  the  condenser 
is  necessary  throughout  the  entire  process.  A  long-stem  funnel 
is  to  be  used  for  delivering  water,  etc.,  into  the  retort,  and  this  is 
especially  necessary  for  the  introduction  of  the  hot  alkaline  per- 
manganate, so  that  none  of  the  reagent  may  enter  the  central  tube 
of  the  condenser  and  foul  the  distillate. 

Seeing  that  the  atmosphere  of  an  ordinary  chemical  laboratory 
contains  quantities  of  NH3,  it  is  well  to  have  a  separate  room  for 
water  analysis. 

In  very  rare  instances  a  potable  water  ma}^  not  yield  the  entire 
free  and  saline  NH3  to  the  first  150  c.c.  of  the  distillate.  In  such 
cases  it  will  be  necessary  to  distil  over  and  Nesslerise  a  fourth  or 
fifth  50  c.c. 


46  PRACTICAL  SANITARY  SCIENCE 

It  is  possible  that  the  '  saline  '  ammonia  exists  in  water  in  con- 
junction with  some  acid,  which,  on  being  boiled  in  the  presence 
of  cai"bonates,  yields  up  the  ammonia  in  the  form  of  (NH4)oC03. 

In  the  second  part  of  the  process,  the  distillation  of  the  albu- 
minoid ammonia  may  require  to  be  carried  to  a  point  at  which 
the  volume  of  fluid  in  the  flask  becomes  dangerously  small;  this 
should  never  be  allowed,  but  ammonia-free  distilled  water  should  be 
added  to  the  flask  as  required,  so  that  the  volume  may  be  kept  up. 

With  regard  to  the  amounts  of '  free  and  saline  '  and  '  albuminoid  ' 
ammonia  which  may  be  allowed  in  different  potable  waters,  there 
is  some  little  difterence  of  opinion.  All  observers  agree  that  the 
two  ammonias  must  be  considered  together,  and  most  agree  that 
in  drinking  waters  if  the  '  albuminoid  '  reach  0-005  part  per  100,000 
the  '  free  and  saline  '  should  not  be  more.  If  the  '  albuminoid  ' 
be  small — say  less  than  0"002  part  per  100,000 — the  '  free  and 
saline  '  may  be  allowed  to  slightly  exxeed  0-005. 

Much  'albuminoid  '  and  little  '  free  and  saline  '  ammonia  indicate 
vegetable  matter;  whereas  much  '  free  and  saline  '  and  little  '  albu- 
minoid '  indicate  animal  matter.  These  indications  must  not  be 
too  literally  rehed  upon. 

As  a  general  rule,  it  ma}^  be  stated  that  where  a  water  has  been 
contaminated  with  sewage  the  high  '  free  and  saline  '  ammonia 
figure  will  be  supplemented  by  an  increase  in  chlorides,  phosphates, 
and  oxidized  nitrogen.  Whilst  accepting  the  principle  that  animal 
pollution  is  indicated  by  a  relatively  larger  figure  for  '  free  and 
saline  '  ammonia  than  for  '  albuminoid,'  and  that  vegetable  matter 
produces  much  '  albuminoid  '  ammonia,  with  little  or  no  '  free,' 
it  must  be  borne  in  mind  that  these  relations  are  liable  to  be  upset. 
Peat}^  waters,  whilst  producing  '  albuminoid '  ammonia  in  quantity, 
should  not  produce  any  '  free  ' ;  still,  there  are  peatj^  waters  met 
with  at  times  which  give  rise  to  a  small  quantity  of  '  free '  ammonia, 
although  no  animal  matter  can  be  traced. 

Good  spring  waters  rarely  contain  '  albuminoid  '  ammonia  above 
0-002  part  per  100,000.  Upland  surface  waters,  as  a  whole,  should 
not  produce  '  free  and  saline  '  ammonia  beyond  o'ooi  part  per 
100,000. 

The  degree  of  initial  dilution  necessary  to  produce  the  best 
colour-tint  for  matching  on  Xesslerisation  can  only  be  discovered 


ORGANIC  MATTER  IN  WATER  47 

by  experience,  and  here,  as  in  all  matters  practical,  the  student 
should  ever  appeal  to  experiment.  Scores  of  waters  must  be 
patiently  worked  out  in  complete  detail  before  he  can  expect  to 
acquire  even  an  elementary  knowledge  of  the  subject. 

Much  '  free  and  saline  '  ammonia  in  the  absence  of  '  albuminoid  ' 
may  be  accounted  for  by  the  water  passing  through  strata  rich  in 
ammonium  salts,  portions  of  which  are  carried  away  in  solution ; 
water-bearing  strata  containing  nitrates  and  subsalts  of  iron  afford 
'  free  and  saline  '  ammonia  by  the  reduction  of  the  nitrates  through 
the  intermediate  phase  of  nitrous  acid  to  NH3;  rain  water  falling 
through  the  atmospheres  of  towns  abounding  in  ammoniacal  fumes 
will  yield  appreciable  quantities  of  '  free  '  ammonia,  and  at  times 
small  quantities  of  '  albuminoid  '  also  from  the  organic  matter  in 
suspension  in  the  air. 

It  may  be  noted  that,  although  the  Wanklyn  process  does  not 
decompose  urea,  the  most  important  and  abundant  nitrogenous 
constituent  of  urine,  nor  recover  NH3  from  a  few  other  bodies  in 
sewage,  still  it  is  of  the  greatest  value  in  dealing  with  the  con- 
tamination of  water  by  organic  matter,  from  the  comparative 
results  afforded,  so  long  as  the  determinations  are  carried  out 
under  similar  conditions. 


Oxidizable  Org'anic  Matter  in  Water. 

Forchammer  applied  to  water  analysis  his  knowledge  of  the  ex- 
perimental fact  that  organic  matter  in  the  presence  of  an  acid  can 
rob  KaMugOg  of  a  portion  of  its  oxygen.  This  process  was  slightly 
modified  by  Tidy,  and  is  usually  known  in  this  country  in  connection 
with  his  name.  It  is  not  a  reliable  test  of  either  the  quality  or 
quantity  of  organic  matter  present,  but,  in  that  pure  waters  absorb 
practically  no  O  from  permanganates  of  potassium,  and  foul  waters 
a  great  deal,  the  process  has  some  value  as  corroborative  evidence 
of  the  presence  of  organic  matter.  It  should  be  noted  that  other 
bodies  beside  organic  matter,  such  as  ferrous  salts,  nitrites,  sul- 
phides, etc.,  abstract  0  from  KaMngOg,  and  when  these  are  present 
they  must  be  accounted  for  before  drawing  a  conclusion  as  to  the 
amount  of  organic  matter  dealt  with.    The  quantity  of  0  absorbed 


48  PRACTICAL  SANITARY  SCIENCE 

varies  with  the  time  of  contact,  the  temperature,  and,  to  less  extent, 
with  the  acidit}-,  and  hght  admitted  during  digestion. 

Potassium  permanganate  in  contact  with  organic  matter  and 
H0SO4  furnishes  5  atoms  of  0  and  colourless  sulphates  of  manganese 
and  potassium. 

KaMuoOg  +  3H.,S04  =  2MnS04  +  K0SO4  +  sHoO  +  5O. 

If  sufficient  acid  be  not  added,  the  liydrated  peroxide  falls  as  an 
opaque  brown  precipitate,  and  only  3  atoms  of  O  are  set  free. 

KjIMnoOg  +  H2SO4  +  3H20=  2Mn{OH)4  +  K2SO4+  3O. 

During  the  digestion  the  reaction  should  be  carefully  watched, 
to  see  that  the  fluid  remains  transparent  throughout.  If  much 
organic  matter  be  present,  it  may  be  necessary  to  add  further  quan- 
tities of  permanganate  from  time  to  time. 

Various  times  and  temperatures  have  been  employed  in  this 
process  for  digesting  the  sample  of  water  with  the  acid  and  per- 
manganate, some  anah'Sts  recommending  four  hours  at  80°  F., 
others  three  hours,  two  hours,  or  fifteen  minutes,  at  higher  and  lower 
temperatures.  In  a  laboratory  where  an  incubator  is  kept  at 
blood-heat  (37°  C.)  it  is  convenient  to  use  it,  and  three  hours  is  a 
sufficient  length  of  time.  In  examinations  two  hours  at  room- 
temperature  may  be  found  most  convenient. 

Prepare  a  standard  solution  of  potassium  permanganate  (i  c.c.= 
O'l  milligramme  of  available  O)  by  dissolving  0-395  gramme  of  the 
pure  crystal  in  a  litre  of  distilled  water.  Make  a  fresh  10  per 
cent,  solution  of  KI,  and  a  fresh  solution  of  sodium  thiosulphate, 
of  about  I  gramme  to  a  litre  of  water.  Lastly,  prepare  a  boiled 
I  per  cent,  solution  of  starch,  and  test  its  delicacy  with  water  con- 
taining the  merest  trace  of  free  iodine. 

Clean  two  Erlenmeyer  flasks  (capacity  150  c.c.  or  less),  and  into 
one  measure  100  c.c.  of  the  water  sample.  Mark  it  '  Sample  '  with 
a  wax  pencil.  Into  the  second,  marked  '  Control,'  measure  100  c.c. 
distilled  water.  Now  carefully  pipette  into  each  10  c.c.  of  the 
standard  solution  of  KoMn^Og,  and  with  another  pipette  run  into 
each  10  c.c.  of  a  25  per  cent,  solution  of  pure  H2SO4.  Stopper  and 
set  aside  in  an  air  oven  or  incubator,  as  the  case  may  be,  at  37°  C. 
for  a  period  of  three  hours.  Should  the  amount  of  organic  matter 
in  the  water  be  large,  the  whole  of  the  permanganate  ma}'  be  de- 


ORGANIC  MATTER  IN  WATER  49 

composed  and  become  colourless;  in  such  a  case  a  second  10  c.c.  of 
the  standard  solution  is  added,  and  should  this  be  decolourized  a 
third,  and  so  on.  Account  of  the  further  additions  will  be  taken 
in  the  calculation  at  the  end  of  the  experiment. 

When  the  time  allowed  has  expired,  and  a  portion  of  the  per- 
manganate remains  undecomposed,  as  demonstrated  by  the  red 
tint  still  to  be  seen,  a  few  drops  of  the  KI  solution  are  added  to  the 
flask  containing  the  water  sample,  when  free  iodine  is  liberated  in 
quantity  proportional  to  the  amount  of  undecomposed  KgMngOs 
remaining.  A  very  few  drops  of  the  KI  solution  will  contain  an 
excess  of  iodine.  This  liberated  I — the  measurer  of  the  undecom- 
posed KaMugOg  left  in  the  Erlenmeyer — is  made  to  oxidize  thio- 
sulphate  run  into  it  from  a  burette,  the  end  reaction  being  definitely 
ascertained  in  the  presence  of  a  few  c.c.  of  the  boiled  starch  solution 
by  the  disappearance  of  the  blue  colour  of  the  iodide  of  starch. 

The  same  procedure  exactly  is  carried  out  with  the  control,  and 
here,  as  no  KaMngOg  has  been  decomposed,  but  the  whole  of  the 
10  c.c.  remains  intact,  we  obtain  a  figure  in  terms  of  c.c.  of  thio- 
sulphate  solution  which  represents  this  amount,  or  i  miUigramme 
available  O. 

The  following  equations  represent  the  liberation  of  free  I  and 
its  subsequent  oxidation  of  sodium  thiosulphate  to  sodium  tetra- 
thionate : 

KaMuaOg  +  loKI  +  8HoS04=  6K2SO4  +  2MnS04  +  SH^O  +  5I2. 
I2  +  aNagSgOg^^  2NaI  +  Na2S40g. 

Example. — The  intact  10  c.c.  standard  solution  of  permanganate 
in  distilled  water  liberated  iodine  equivalent  to  27  c.c.  of  the  thio- 
sulphate solution.  The  undecomposed  portion  of  the  10  c.c.  of 
standard  permanganate  in  the  water  sample  liberated  iodine  equiva- 
lent to  23-2  c.c.  of  thiosulphate.  From  this  it  is  plain  that  the 
amount  of  permanganate  solution  decomposed  by  the  organic 
matter  (assuming  that  no  nitrites,  sulphides,  etc.,  were  present)  is 
represented  by  27-23-2  c.c.  thiosulphate.  But  10  c.c.  standard 
permanganate  or  i  milligramme  0=  27  c.c.  thiosulphate; 

.•.27  :  27-23-2  :  :  i  milhgramme  :  x\ 

(27-23-2)  XI 

x=  ^-' '^—^ =  0-14. 

27 


50  PRACTICAL  SAXITARY  SCIENCE 

There  is,  therefore,  in  lOO  c.c.  of  this  water  organie  matter  capable 
of  absorbing  from  pemianganatc  of  potassium  O  to  the  extent 
of  0-14  milHgramme,  or  0-14  part  per  100,000,  under  the  conditions 
of  time  and  temperature  employed. 

If  it  be  desired  to  obtain  some  indication  of  the  nature  of  the 
reducing  substances,  two  samples  of  the  water  may  be  treated  with 
the  standard  permanganate,  one  at  37°  C.  for  fifteen  minutes,  and 
the  other  for  three  hours  at  the  same  temperature.  Nitrites,  ferrous 
salts,  and  sulphuretted  hydrogen  effect  reduction  almost  imme- 
diately, whilst  a  relatively  large  amount  of  ordinar}'  organic  matter 
reduces  the  reagent  only  after  a  considerable  time. 

The  O  absorbed  from  permanganate  is  higher  as  a  rule  in  upland 
surface  waters  than  in  waters  from  other  sources;  and  whilst  no 
strict  standards  can  be  insisted  on,  it  may  be  stated  generally  that 
in  upland  surface  samples  of  great  purity  this  figure  in  parts  per 
100,000  (time  three  hours,  temperature  37°  C.)  will  not  exceed  o-i, 
in  waters  of  medium  purity  0-3,  and  in  waters  of  doubtful  purity  0*4. 
The  corresponding  figures  for  other  sources  will  not  exceed  0-05, 
0-15,  and  0-2 


CHAPTER  V 

OXIDIZED  NITROGEN— NITRITES  AND  NITRATES 

During  the  early  stages  of  putrefaction  of  organic  matter  much 
free  N  escapes  in  gaseous  form,  and  the  rest  unites  with  H  to  form 
NHg.  As  has  been  already  stated,  certain  bacteria  in  the  soil  and 
elsewhere  convert  NH3  into  HNO2,  which  latter  combines  with 
various  bases  to  form  nitrites.  Of  the  so-called  '  nitrous  '  organisms 
several  species  have  been  studied,  one  of  which  is  the  Nitrosomonas 
of  Winogradsky.  Nitrites,  therefore,  represent  chemicallj'  the 
intermediate  stage  in  the  process  of  oxidation  or  purification. 
Under  certain  conditions,  to  be  presently  mentioned,  they  also 
represent  an  intermediate  stage  in  the  reduction  of  nitrates  to 
NHg.  The  presence  of  nitrites  in  a  water  indicates  more  remote 
contamination  in  point  of  time  or  space,  or  of  both,  than  does  NH3. 

In  like  manner  '  nitric  '  organisms,  such  as  the  Nitrobacier  (Wino- 
gradsky), transform  HNOg  into  HNO3,  which  readily  becomes 
nitrates.  This  class  of  bacteria  has  no  action  on  NH3,  and  the 
previous  class  is  unable  to  carry  the  oxidation  of  NH3  further  than 
HNO2,  so  that  two  distinct  and  independent  types  of  organism  are 
necessary  to  the  complete  oxidation  of  NH3. 

It  will  be  readily  seen  that  the  detection  and  estimation  of 
nitrites  and  nitrates  are  of  considerable  importance  in  the  investiga- 
tion of  the  problem  of  organic  pollution. 

The  presence  of  nitrates  alone  in  a  water  indicates  previous 
pollution  that  has  been  oxidized  and  rendered  harmless.  But 
if  the  quantity  of  nitrates  be  great,  purified  sewage  may  be  sus- 
pected, which,  through  a  breakdown  at  any  moment  in  the  machinery 
of  purification,  may  become  most  dangerous  sewage.  Moreover,  in 
view  of  the  fact  that  sewage  effluents  contain  almost  as  man}-  micro- 
organisms as  crude  sewage,  no  effluent,  however  high  its  degree  of 

51 


52  PRACTICAL  SAXITARY  SCIENCE 

purification  may  be  chemically,  should  ever  be  allowed  to  come 
in  contact  with  drinking  water.  In  all  waters  possessing  a  high 
nitrate  figure  this  possibility  of  the  presence  of  purified  sewage 
should  be  borne  in  mind. 

When  nitrates,  which  form  the  end  of  the  purification  of  organic 
matter,  occur  alone  it  is  obvious  that  no  indication  of  the  date 
of  the  previous  pollution  is  given. 

In  determining  the  true  significance  of  nitrates  in  potable  waters 
it  is  necessary  to  consider  (i)  whether  they  arise  from  geological 
strata  (chalk,  lias,  oolite,  sandstones)  through  which  the  water  has 
percolated,  in  which  case  the  evidence  of  organic  pollution  supplied 
by  the  other  steps  of  the  analj^sis — such  as  the  '  free  and  saline  ' 
NH3,  '  albuminoid  '  NH3,  O  absorbed  from  permanganate  of  potas- 
sium, etc. — will  be  negative;  (2)  whether  they  are  due  to  purified 
sewage,  in  which  case  the  quantity  will  be  much  too  great,  as  also 
that  of  CI;  (3)  whether  they  represent  a  small  amount  of  organic 
matter  that  has  undergone  complete  oxidation,  and  is  to  be  con- 
sidered harmless.  In  this  case  the  quantity  will  be  small — in  rain 
and  upland  surface  waters  not  exceeding  o-i  part  per  100,000 — and 
all  the  other  items  of  the  analysis  employed  to  discover  organic 
matter  will  afford  negative  evidence. 

In  the  few  cases  where  strata  alone  contribute  soluble  nitrates 
the  quantity  will  rarely  exceed  0-5  part  per  100,000,  but  no  figures 
can  be  laid  down  as  an  accurate  standard,  and  each  case  must  be 
worked  out  in  connection  with  the  rest  of  the  analytical  data. 

In  a  few  instances  strata  containing  nitrates  (in  particular  the 
lower  greensand)  contain  also  reducing  minerals,  such  as  proto- 
salts  of  iron,  which  reduce  HNO3  to  HNOg,  and  the  latter  to  NH3. 
The  same  reduction  can  be  effected  by  denitrifying  micro-organisms. 
Free  XH3,  due  to  reduction  of  nitrates  and  nitrites,  will  be  identified 
by  the  absence  of  organic  NH3,  and  all  other  evidence  of  organic 
pollution. 

Nitrites  are  very  unstable,  and  in  the  presence  of  available  O 
rapidlv  become  nitrates.  In  the  early  stages  of  the  oxidation  of 
large  quantities  of  animal  organic  matter  they  are  mostly  found  in 
company  with  NHg,  but  a  foul  water  may  at  a  particular  moment 
fail  to  furnish  any  nitrites.  They  are  significant  of  recent  con- 
tamination, except  in  those  cases  just  mentioned,  where  they  are 


OXIDIZED  NITROGEN— NITRITES  AND  NITRATES      53 

due  to  the  reduction  of  nitrates  in  strata.  Nitrites,  then,  which 
in  deep-well  waters  may  be  merely  the  products  of  reduction  of 
nitrates  by  iron  in  strata,  iron  pipes,  etc.,  and  consequently  quite 
harmless,  will  in  shallow  wells  and  surface  supplies  condemn  the 
water. 

All  the  inorganic  N — apart  from  strata — found  in  nitrates, 
nitrites,  free  and  sahne  NH3,  after  deducting  that  present  in  rain 
water,  may  be  regarded  as  due  to  previous  sewage  contamination. 

Detection  and  Estimation  of  Nitrites. 

Potassium  Iodide  and  Starch.— To  lo  c.c.  of  the  water  in  a 
test-tube  add  i  c.c.  of  a  clear  and  boiled  i  per  cent,  starch  solution 
and  a  drop  of  KI  solution.  Mix  and  add  a  little  dilute  H2SO4,  when 
immediately  a  blue  colour  is  produced  if  nitrites  be  present  in  con- 
siderable amount.  On  standing,  nitrates  give  this  reaction  also 
Pure  sulphuric  acid  should  be  used,  and  it  is  found  that,  owing  to  the 
instability  of  KI,  Znl  gives  better  results.  This  test  can  be  made  a 
quantitative  colorimetric  one  by  operating  on  100  c.c.  of  the  water 
in  a  Nessler  glass,  and  in  a  second  Nessler  100  c.c.  of  a  mixture  of 
distilled  water  and  the  amount  of  a  standard  nitrite  necessary  to 
form  a  colour  match.  When  the  proportion  of  nitrites  in  a  sample 
is  I  in  10,000,000,  the  blue  colour  is  formed  in  a  few  minutes;  when 
I  in  100,000,000,  in  twelve  hours;  and  when  i  in  1,000,000,000, 
in  forty-eight  hours.     Lintner's  soluble  starch  should  be  used. 

Griess's  Method.  —  Make  a  5  per  cent,  solution  of  meta- 
phenyleije-diamine  in  water.  Decolourize  with  animal  charcoal, 
and  render  slightly  acid  with  H2SO4.  Much  acid  must  not  be 
used.  To  100  c.c.  of  the  water  to  be  tested  in  a  Nessler  glass  add 
I  c.c.  of  the  reagent,  cover,  and  set  aside  in  a  warm  place  for  twenty 
minutes.  A  yellow  to  orange  colour  is  produced,  according  to  the 
quantity  of  nitrites  present.  The  reagent  should  be  made  at  the 
time  of  use.  When  metaphenylene-diamine  (diamido-benzol)  reacts 
with  nitrous  acid,  triamido-azo-benzol  (Bismark brown)  is  produced; 
hence  the  colour. 

2C6H4(NH2)2  +  HN02=  C6H4(NH2)N.C6H3(NH2)oN  +  2H0O. 

By  using  a  standard  solution  of  potassium  nitrite,  the  colour 
produced  in  the  100  c.c.  of  water  may  be  matched  in  the  same 


54  PRACTICAL  SAXITARY  SCIEXCE 

quantity  of  distilled  water.  A  series  of  trials  must  be  made,  in 
which  the  reagent  is  added  to  the  contents  of  the  two  cylinders  at 
the  same  moment,  and  the  cylinders  covered  and  set  aside  in  a 
warm  place  for  twenty  minutes.  The  standard  nitrite  is  prepared 
thus:  Dissolve  0-406  gramme  of  AgNO^  in  boiling  water;  add  shght 
excess  of  KCl.  Silver  chloride  is  formed,  and  gradually  falls  to  the 
bottom.  ]\Iake  up  to  a  litre  and  allow  to  settle.  When  clear, 
decant  off  the  supernatant  fluid,  and  dilute  each  100  c.c.  up  to  a 
litre.  It  should  be  kept  in  the  dark  and  in  small  bottles  filled  to 
the  stopper,  so  as  to  protect  it  from  the  air. 

I  c.c. =  0-01  milligramme  NgOg. 

,  ,^„      /mol.  wt.  NO.,  \ 

=  0-000        ,,  N0o=( — -, — ^  XT  ^"  X  O'Oi  )■ 

-     Vmol.wt.NoOg  / 

-,      /mol.  wt.   Np  \ 

=  0-0037       "  N,=  l — , — .  ^.  „-xo-oi ). 

^'  -     \mol.wt.N2O3  / 

Detection  and  Estimation  of  Nitrates. 

Brucine  Test. — To  10  c.c.  of  the  water  in  a  test-tube  add  i  c.c, 
of  a  saturated  solution  of  brucine,  and  shake.  Incline  the  test-tube 
and  pour  down  the  side  2  c.c.  of  pure  H^SO.j.  Carefully  bring 
the  test-tube  to  the  vertical  against  a  white  ground.  A  pink  zone 
is  foiTned  at  the  junction  of  the  acid  and  supernatant  mixture, 
which  lasts  for  a  few  seconds,  and  then  changes  to  brownish  yellow. 
When  nitrates  are  in  large  quantity,  the  colour  changes  very  rapidly. 
Where  the  reaction  is  doubtful,  a  fresh  layer  of  the  mixture  can  be 
brought  in  contact  with  the  acid  by  imparting  to  the  test-tube  a 
slight  centrifugal  motion. 

Or,  10  c.c.  of  the  water  ma)^  be  evaporated  to  dryness  in  a  platinum 
dish,  a  drop  of  pure  H2SO4  added,  and  a  small  crj^stal  of  brucine 
dropped  on  the  contents,  when  a  pink  colour  will  appear,  even  where 
the  quantity  of  nitrates  is  so  small  as  o-oi  part  per  100,000. 

Diphenylamine  Test. — Mix  about  10  milligrammes  of  diphenyl- 
amine  with  i  c.c.  pure  H.2SO4  in  a  porcelain  basin,  and  carefully 
run  I  c.c.  of  the  water  over  the  mixture.  A  blue  colour  develops 
in  the  presence  of  nitrates ;  the  depth  of  the  tint  is  roughly  propor- 
tional to  the  amount  of  nitric  acid.  This  reaction  is  not  simulated 
by  any  other  constituent  of  potable  waters. 


OXIDIZED  NITROGEN—NITRITES  AND  NITRATES      55 

Crum's  Quantitative  Method. — This  method  consists  in  shaking 
up  the  residue  obtained  from  the  concentration  of    a  measured 
quantity  of  the  water  with  metalHc    mercury  and  pure   H2SO4, 
when  nitric  oxide  is  produced,  which  is  afterwards  conducted  to  a 
gas  analysis  apparatus  and  measured.     It  requires  some  experience 
in  collecting  and  measuring  gases,  but  in  the  hands  of   a  skilled 
operator  is  one  of  the  most  exact  methods  known.     The  nitric 
oxide  produced  represents   the   N   of   nitrites   and   nitrates.     To 
obtain  the  N  due  to  nitrates  alone,  that  obtained  for  nitrites  by 
Griess's  method  is  subtracted  from  the  total.     This  method  may  be 
used  for  the  estimation  of  nitrous  and  nitric  N  in  sewage  effluents. 
Process  of  Estimation. — Evaporate  to  dryness  in  a  dish  100  c.c. 
of  the  water.     Add  a  small  quantity  25  per  cent.  H2SO4.     Heat  the 
dish  to  remove  CO2  from  any  carbonate  present,  and  if  the  volume 
of  the  liquid  exceeds  2  c.c.  evaporate  down  to  that  volume.     Fill 
the  nitrometer  with  Hg,  and  pour  the  contents  of  the  dish  into  the 
cup  of  the  nitrometer,  rinsing  out  with  a  very  small  quantity  of 
the   dilute   H2SO4.     Now  run   the   liquid    through   the   stopcock, 
taking  care  that  no  air  enters.      Run  through  also  about  twice  the 
volume  of  pure  concentrated  H2SO4,  and  shake  so  as  to  cause  part 
of  the  Hg  to  mix  with  the  hot  liquid.     In  a  short  time  NO  will  be 
liberated.     Continue  the  shaking  till  gas  ceases  to  come  off  (five  to 
ten  minutes).     Cool  to  the  temperature  of  the  air.     x\djust  mercury 
levels,  and  take  the  reading.     Note  atmospheric  temperature  and 
pressure,  and  calculate  weight  of  N  in  volume  of  NO  obtained. 

An  estimation  gave  2  c.c.  NO;  temperature  18°  C;  pressure 
758  millimetres. 

^^^S32^=,.87NOatN.T.P. 

291 X  760  ' 

As  NO  contains  half  its  volume  of  N,  and  weight  of   i  c.c.  H  = 

^    ^  ^o                   j-u         ■  1,1.    r  XT  •    ^1-    xT^     1-87  X  o-oooo8o  X 14 
0-000089  gramme,  the  weight  of  N  m  the  N0=  — -  = 

0-001165  gramme^  1-165  part  per  100,000  N  in  the  water. 

From  this  subtract  the  weight  of  nitrous  N  found  by  Griess's 
method;  the  remainder  is  that  due  to  nitrates. 

CoppeP-Zinc  Couple  Method.— This  method  estimates  nitrous 
and  nitric  N  as  NH3.  In  calculating  the  nitric  N,  it  is  plain  that 
from  the  amount  of  NH3  obtained  in  the  process  deduction  must 


56  PRACTICAL  SAXITARY  SCIENCE 

be  made  for  original  NH.,  in  the  water  as  well  as  that  derived  from 
nitrites. 

^^'hen  zinc  is  immersed  in  CuSOj  solution,  a  spongy  deposit  of 
Cu  is  precipitated  upon  it,  and  in  this  condition  it  is  capable  of 
bringing  about  various  decompositions  in  which  H  is  liberated. 
The  H  is  occluded  by  the  spongy  copper,  and  when  thus  occluded 
reduces  nitrates  to  nitrites,  and  nitrites  to  ammonia.  The  reaction 
is  hastened  by  the  presence  of  traces  of  NaCl  and  other  salts,  rise 
of  temperature,  and  any  condition  which  increases  the  electrolytic 
action  of  the  couple. 

Take  a  piece  of  clean  zinc-foil  and  cover  it  with  3  per  cent. 
CUSO4  solution  until  a  copious,  firmly-adherent  coating  of  black 
spongy  Cu  has  been  deposited.  This  deposition  should  not  be 
pushed  too  far,  otherwise  the  Cu  will  be  so  easily  detached  that  it 
cannot  be  washed.  When  sufficient  deposit  has  accumulated,  the 
CUSO4  solution  is  removed  and  the  couple  carefully  washed  with 
distilled  water,  when  it  is  ready  for  use.  A  clean,  wide-mouthed, 
stoppered  bottle  is  selected  and  washed  out  with  some  of  the  water 
to  be  tested.  The  coated  foil  is  inserted,  and  a  measured  quantity 
— say  100  c.c. — of  the  water  poured  in  so  that  the  foil  is  completely 
covered.  The  bottle  is  tightly  stoppered  and  set  aside  in  a  warm 
place  for  some  hours.  If  the  bottle  be  properly  closed,  the  tempera- 
ture may  be  raised  to  28°  or  30°  C.  without  fear  of  losing  NH3. 
When  it  is  desirable  to  hasten  the  reaction,  a  little  NaCl  may  be 
added  to  the  water  (o-i  gramme  to  100  c.c),  or  COg  ma}'  be  passed 
through  the  water  before  it  is  placed  in  the  bottle.  In  calcareous 
waters  lime  may  be  removed  by  the  addition  of  some  pure  oxalic 
acid  previous  to  digestion  with  the  couple.  Nitrous  acid  remains 
in  the  solution  until  the  reaction  is  complete,  so  that  it  is  necessary 
to  test  a  small  quantity  of  the  water  from  time  to  time  by  Griess's 
reagent  for  the  presence  of  this  body.  Metaphenylene-diamine 
easily  detects  i  part  of  nitrous  acid  in  10,000,000  of  water.  When 
the  last  trace  of  nitrous  acid  has  disappeared,  the  water  is  poured 
off  the  couple  into  a  clean,  stoppered  bottle,  and  if  turbid  allowed  to 
subside.  A  portion  of  the  clear  fluid,  diluted  if  necessary  according 
to  the  degree  of  concentration  of  the  nitrates  in  the  water,  is  trans- 
ferred to  a  Nessler  glass  and  the  NHg  estimated  in  the  usual  manner. 
In  the  case  of  coloured  waters,  or  those  containing  magnesium  and 


OXIDIZED  NITROGEN— N ITU ITKS  AND  NITRATES      57 

other  salts  that  interfere  with  the  Nessler  reagent,  a  measured 
quantity  of  the  water  poured  off  the  couple  should  i)c  put  in  a 
retort,  a  httle  NagCOg  added,  and  Nesslerisation  performed  on  the 
distillate.  It  has  been  found  that  about  half  a  square  decimetre  of 
zinc-foil  should  be  used  for  each  100  c.c.  of  a  water  containing 
5  or  less  parts  of  nitric  acid  per  100,000.  A  larger  proportion  of 
foil  should  be  used  for  waters  richer  in  nitrates  and  for  sewage 
effluents.  The  couple,  if  carefully  washed  after  use,  may  be  used 
for  at  least  three  estimations.  It  is  convenient  in  most  laboratories 
to  digest  overnight.  Where  accurate  results  are  required,  and 
in  the  hands  of  the  inexperienced,  it  is  advisable  to  distil  the  water 
removed  from  the  couple  and  estimate  the  ammonia  in  the  dis- 
tillate. From  the  total  N  found  as  NH3  deduct  that  due  to  inorganic 
NH3  found  by  Wanklyn's  process,  and  that  due  to  nitrites  found  by 
Griess's  process;  the  remainder  is  the  N  due  to  nitrates  in  the 
water. 

Sprengel's  Phenol  Method.^ — This  is  a  much  less  accurate 
method  (error  of  under-estimation),  but  can  be  performed  in  a 
limited  time.  It  estimates  the  N  of  nitrates  alone,  and  is  chiefly 
appHcable  to  waters  containing  small  quantities  of  nitric  acid. 
When  phenol  sulphonic  acid  reacts  with  nitric  acid,  picric  acid 
(trinitro-phenol)  is  formed. 

C6H3(OH)H2S03  +  3HN03=  2H2O  +  H2SO4+  QH^NOaJgOH, 

and  the  ammonium  salt  of  picric  acid  being  yellow,  this  body 
lends  itself  to  quantitative  colorimetric  estimation. 

C6H2(N02)30H  +  NH40H=  C6H2(N02)30NH4  +  H2O. 

The  solutions  required  are: 

Standard  potassium  nitrate,  containing  0-7215  gramme  KNO3  in 
a  litre  of  water.  One  c.c.  of  this  solution=o-i  milligramme  N. 
A  dilution  of  100  c.c.  to  a  litre  should  be  made  for  the  analysis.  One 
c.c.  will  then  contain  o-oi  milligramme  nitric  N. 

Phenol  Sulphonic  Acid. — ^The  phenol  sulphonic  acid  used  should 
be  the  pure  disulphonic  acid  (CgH3(OH)H2S03),  which,  with  HNO3, 
gives,  according  to  Kekule,  picric  acid  even  in  the  cold.  Three 
grammes  pure  phenol  and  37  grammes  (20*1  c.c.)  pure  H2SO4, 
specific  gravity  1-84,  are  mixed  in  a  beaker  and  heated  for  six  hours 


58  PRACTICAL  SANITARY  SCIENCE 

on  a  water  bath  at  ioo°  C.  Should  the  acid  thus  formed  crys- 
tallize out  on  standing,  it  may  be  brought  into  solution  bv  reheating 
for  a  short  time. 

Process. — Place  lo  c.c.  of  the  water  in  a  porcelain  basin  on  a 
water  bath  and  in  a  similar  basin  lo  c.c.  of  the  standard  nitrate; 
when  just  dry,  add  to  each  i  c.c.  of  the  phenol  sulphonic  acid  and 
allow  to  remain  for  a  few  minutes  on  the  bath.  Now  transfer  to 
two  Nessler  glasses  the  contents  of  the  dishes,  and  wash  out  with 
25  per  cent,  ammonia  solution  the  last  trace  of  material  from  the 
dishes;  add  further  ammonia  to  the  Nesslers  until  all  effervescence 
ceases  and  a  small  excess  of  ammonia  is  found  in  each.  Spirting 
ma}'  be  prevented  by  washing  out  the  contents  of  the  basins  into 
the  Nessler  glasses  with  a  small  quantity  of  distilled  water,  and 
adding  the  ammonia  solution  afterwards.  Make  up  to  100  c.c.  in 
both  cases  with  distilled  water,  and  let  stand  for  fifteen  minutes. 

In  performing  the  estimation,  take  a  third  Nessler  glass  and 
pipette  into  it  from  the  more  deeply-coloured  cylinder  (which  is 
generally  that  containing  the  standard  nitrate)  a  quantity  deemed 
necessary  to  match  the  tint  of  the  cylinder  containing  the  water 
sample.  Make  up  to  100  c.c.  with  distilled  water,  and  compare  the 
tints  on  a  white  tile.     An  exact  match  can  be  effected  in  a  few  trials. 

Suppose  that  20  c.c.  from  the  standard  soliition  match  the  water 
sample,  the  latter  contains  y%°„  of  the  N  as  nitrates  contained  in 
the  standard.  Each  c.c.  of  the  standard  contains  o'oi  milli- 
gramme N. 

.•.  10  c.c.  =  0-1  milligramme  N,  but  y-^"jj  of  o-i  =  o-02; 

.'.  10  c.c.  water  under  examination  =0-02  milligramme  N; 

•  ■.  100  ,,         .,  ,,  ,,         =0-2 

or  this  water  contains  0-2  part  nitric  N  per  100,000. 

In  the  case  of  very  good  waters  20,  50  or  more  c.c.  should  be 
evaporated  to  dryness  as  above,  and  only  5  c.c.  of  the  standard 
nitrate  taken. 

The  amount  of  sulphonic  acid  used,  so  long  as  there  is  enough, 
is  of  little  import.  In  comparing  the  colours,  the  best  results  are 
obtained  when  the  intensity  of  the  colour  does  not  exceed  that  pro- 
duced by  I  c.c.  of  a  water  containing  about  0-05  part  N  per  100,000. 
The  colour  produced  by  o-i  part  per  100,000  is  difficult  to  match 
accurately.     The  loss  of  N  during  evaporation  is  less  when  the 


OXIDIZED  NlTROGEN—NITIirrES  AND  NITRATES      59 

evaporation  is  made  to  take  place  rapidly  in  an  op(,'n  dish  at  100''  C. 
Slow  evaporation  at  a  lower  temperature  causes  more  loss,  and 
the  dry  residues,  if  further  heated,  lose  N.  Chlorine  does  not 
interfere  if  present  in  less  quantity  than  2  parts  per  100,000.  If  it 
exceed  7  parts,  it  should  be  removed  before  evaporation  by  Ag2S04. 
This  process  does  not  estimate  the  N  as  nitrite,  as  the  action  of 
nitrous  acid  results  in  the  formation  of  nitroso-phenol,  CeH4(N0)0H, 
which  is  colourless  in  dilute  solutions. 


CHAPTER  VI 

GASES    IN   WATER— WATER    SEDIMENT— INTERPRETATION 
OF  RESULTS  OF  CHEMICAL  ANALYSES 

Water  dissolves  gases  in  quantities  depending  on  temperature, 
pressure,  and  solubility  of  the  gas.  The  principal  gases  found  in 
potable  waters  are  N,  0,  COo,  and  occasionally  CHj,  HoS,  and  NH3. 
Of  these  O  and  CO2  are  alone  worthj^  of  estimation.  As  organic 
matter  in  water  throughout  all  its  stages  of  change  lays  hold  of 
dissolved  oxj'gen,  the  presence  or  absence  of  this  gas  may  afford 
valuable  infomiation  regarding  such  organic  material.  These 
remarks  apply  equally  to  sewage  effluents. 

From  a  hygienic  point  of  view  the  subject  of  gas  extraction  from 
waters  is  not  sufficiently  important  to  warrant  the  expenditure  of 
time  and  labour  inseparable  from  accurate  gasometric  work.  Nor 
is  the  information  gained,  even  when  the  work  is  most  exactly 
performed,  of  constant  or  certain  value. 

Estimation  of  0  Dissolved  in  Water  (Thresh). 

When  sulphuric  acid  is  added  to  a  mixture  of  KI  and  a  nitrite, 
iodine  is  set  free.  If  0  be  carefully  excluded,  this  free  iodine 
rapidly  reaches  its  maximum,  and  remains  constant.  But  if  O 
be  admitted,  the  amount  of  iodine  liberated  varies  with  the  time  of 
exposure,  and  has  no  relation  to  the  amount  of  nitrite  present. 
Thresh  concludes  that  the  NO  produced  acts  as  a  carrier  of  O, 
forming  N2O3,  which  liberates  more  iodine  and  is  again  trans- 
formed into  NO,  and  that  this  action  continues  as  long  as  any 
free  dissolved  O  remains  in  the  water, 

2NaNOo  +  2H.,S04  +  2KI  =  K,S04  +  NaoS04  +  2HNO2  +  2HI, 
2HI  +  2HN0.=  I,  +  2H,0  + 2NO. 

2X0  +  d=N.,0,- 
N2O3  +  2HI  =  2Nd  + 12  +  H2O. 

L,  +  2Na2S203  =-  2NaI  +  Na2S406. 

60 


GASES  IN  WATER 


6l 


In  the  above  reactions  it  will  be  noted  that  free  nitrous  acid  is 
first  formed,  and  that  this  liberates  I. 

If  now  the  total  amount  of  I  liberated  be  determined,  and  the 


Fig.  4. 

amount  of  I  theoreticalh^  hberated  by  the  nitrite  be  calculated,  the 
difference  will  represent  the  I  liberated  b}^  the  O  dissolved  in  the  water. 
The  estimation  is  carried  out  as  follows  (see  Fig.  4) : 


62  PRACTICAL  SAXITARY  SCIENCE 

Into  a  wide-mouthed  glass  bottle  A,  of  500  c.c.  capacity,  is  fitted 
an  indiarubber  cork,  with  four  perforations.  The  stem  of  a  separ- 
ator funnel  B,  holding  about  300  c.c.  of  the  water,  is  pushed  through 
the  cork.  Through  another  perforation  is  run  a  piece  of  glass  tube 
attached  b}'  rubber  tubing  to  the  lower  end  of  a  100  c.c.  burette  C, 
graduated  to  tenths  of  a  c.c.  Through  the  remaining  two  per- 
forations are  run  pieces  of  glass  tubing  bent  at  right  angles,  one  D, 
connected  by  rubber  with  a  gas-tap,  and  the  other  E,  by  similar 
tubing  with  a  short  piece  of  glass  tube  thrust  through  an  india- 
rubber  cork,  which  fits  the  top  of  the  separator  funnel.  The 
funnel  B  is  filled  with  water  to  the  top,  and  the  glass  stopper 
inserted,  displacing  a  small  quantity  of  water.  The  contents  are 
accuratel}^  measured  once  for  all,  and  the  capacity  of  the  funnel 
noted. 

The  funnel  is  now  filled  with  the  w'ater  to  be  examined.  The 
burette  C  is  charged  with  thiosulphate  (i  c.c.  =  0*25  milligramme  0), 
made  by  dissolving  775  grammes  of  crystalline  sodium  thiosulphate 
in  a  litre  of  distilled  water. 

[2NaoS203.5  H.O  + 1,  -  2NaI  +  NaoS^Og- 

"  ^    "    i;=o. 

496  = 16 

31  =    I 

775  =   0-25]. 

Having  thoroughly  cleaned  and  dried  the  bottle  A,  the  cork  is 
inserted  and  the  tube  connected  with  the  lower  end  of  the  burette  C, 
fixed  in  position.  The  funnel  B  is  filled  up  to  the  top,  and  the 
stopper  inserted;  the  stopper  is  now  taken  out  and  i  c.c.  of  a  solu- 
tion of  sodium  nitrite  and  potassium  iodide  (sodium  nitrite  0*5 
gramme,  KI  20  grammes,  distilled  HoO  100  c.c.)  poured  in  from  a 
I  c.c.  pipette.  From  a  second  i  c.c.  pipette  is  run  in  i  c.c.  H2SO4 
{25  per  cent.).  The  higher  specific  gravity  of  the  nitrite  mixture 
and  of  the  HoSOj  solution  causes  these  to  sink  rapidly  to  the  bottom 
of  B,  and  when  the  stopper  is  replaced  a  negligible  quantity,  if  any, 
of  the  reagents  just  added  is  lost  in  the  small  amount  of  water 
which  overflows;  in  this  way  the  entry  of  air  is  excluded.  The 
funnel  is  inverted  a  few  times,  so  as  to  effect  a  uniform  admixture, 
and  its  nozzle  pushed  through  the  cork.  The  tube  D  is  joined  up 
with  a  gas-tap,  and  gas  rapidly  passed  through  the  bottle.     When 


GASES  IN  WATER  63 

all  the  air  has  been  expelled  the  gas  may  be  lighted  at  the  end  of  E, 
where  it  will  burn  quietly.  The  stopper  of  B  is  removed,  and 
having  rapidly  extinguished  the  flame  at  the  end  of  E,  the  cork  of 
the  latter  is  fixed  in  B,  after  which  the  tap  is  turned,  and  the  mixture 
of  water  and  nitrite  solutions  is  discharged  into  A.  The  tap  of  B 
is  now  turned  off,  the  cork  at  the  end  of  E  removed,  and  the  gas 
relighted  and  turned  down  to  a  small  flame.  Thiosulphate  is  then 
run  in  slowly  from  C  until  the  brown  colour  produced  by  the 
liberated  iodine  is  nearly  removed.  About  3  c.c.  of  a  fresh  starch 
solution  is  poured  into  B,  and  i  c.c.  of  this  carefully  run  through 
the  tap  into  A,  in  order  to  definitely  fix  the  end  of  the  reaction. 
As  the  blue  colour  returns  in  most  instances  after  a  few  seconds,  it 
is  well  to  wait  for  a  little  and  add  a  further  drop  or  two  of  thio- 
sulphate to  complete  the  decolorization. 

The  amount  of  thiosulphate  used  will  represent : 

(i)  The  I  (and  accordingly  its  equivalent   as  0)  liberated  by 
the  nitrite  in  the  reagent. 

(2)  The  I  (and  its  equivalent  O)  liberated  by  the  nitrite,  if  any, 

originally  in  the  water. 

(3)  The  O  dissolved  in  the  reagents. 

(4)  The  0  dissolved  in  the  water  sample. 

The  value  of  (4)  can  obviously  be  determined  by  subtracting 
the  sum  of  the  values  (i),  (2),  and  (3)  from  the  total. 

The  values  of  (i)  and  (3)  can  be  easily  determined  by  making  a 
blank  experiment,  using  five  times  the  amounts  of  nitrite-iodide 
solution,  sulphuric  acid,  and  distilled  water  in  lieu  of  thiosulphate, 
as  it  may  be  assumed  that  the  oxygen  in  distilled  water  is  equal 
to  that  in  thiosulphate.  The  number  of  c.c.  of  thiosulphate  solution 
required  divided  by  5  gives  the  joint  values  of  (i)  and  (3).  In 
order  to  estimate  (2)  the  nitrous  acid  in  the  sample  must  be  very 
carefully  determined,  and  as  94  parts  by  weight  of  this  are  equiva- 
lent to  16  of  O,  the  calculation  is  easily  made  [2HN02- — >0]. 

For  a  given  piece  of  apparatus,  the  values  of  (i)  and  (3)  having 
been  once  determined,  it  is  unnecessary  to  repeat  the  process, 
granted  that  the  same  quantities  of  reagents  are  always  used. 
In  (2)  the  nitrous  acid  may  be  estimated  by  Griess's  method. 

A  simpler  method  for  the  estimation  of  0  dissolved  in  water  is 
that  of  Winkler : 


64  PRACTICAL  SAX  IT  A  RY  SCIENCE 

In  this  method  manganous  hydrate  serves  as  the  oxygen  carrier, 
and  enables  it  to  hberate  its  equivalent  of  iodine,  which  is  then 
titrated  in  the  usual  way. 

In  collecting  the  sample  of  water,  care  must  be  taken  to  avoid 
agitating  it  and  exposing  it  for  any  length  of  time  to  the  air.  It  is 
transferred  with  similar  precautions  by  syphoning  to  a  stoppered 
bottle  of  known  capacity — say  250  c.c.  One  c.c.  of  strong 
manganous  chloride  solution  (40  grammes  MnClo.HoO  to  100  c.c.) 
and  2  c.c.  of  a  solution  containing  33  per  cent.  KOH  and  10  per  cent. 
KI  are  introduced  by  a  pipette  with  long  stem  which  carries  its 
contents  to  the  bottom,  thus  displacing  3  c.c.  of  water  from  the  top. 
The  bottle,  which  must  be  full  of  liquid,  is  now  closed  with  the 
stopper  without  including  any  air-bubble,  and  the  liquids  are 
mixed  b}'  several  times  inverting  the  bottle.  The  manganous 
hydroxide  precipitate  which  forms  will  be  more  or  less  discoloured 
by  higher  hydroxide,  according  to  the  proportion  of  O  which  was 
dissolved  in  the  water  sample.  As  the  oxidation  of  the  manganous 
hvdroxide  is  not  immediate,  and  the  result  is  influenced  by  light, 
the  bottle  is  put  aside  in  a  dark  cupboard  for  fifteen  minutes;  5  c.c. 
strong  HCl  aie  added,  which  cause  the  precipitate  to  disappear, 
and  leaves  the  liquid  coloured  with  dissolved  iodine.  The  iodine 
is  titrated  with  standard  thiosulphate,  of  which  the  oxygen  value 
should  be  known,  so  as  to  give  the  amount  of  oxygen  directly. 
If  250  c.c.  of  water  be  used,  it  will  be  convenient  to  use  a  solution  of 
thiosulphate  of  775  grammes  to  the  litre  [i  c.c. =  0-25  milligramme 
O],  as  then  each  c.c.  thus  used  can  be  read  as  i  milligramme  O 
dissolved  per  litre  of  water.  It  is  usual,  however,  to  determine 
the  amount  of  thiosulphate  required  by  the  same  volume  of  fully 
aerated  pure  water  of  similar  character,  or  of  distilled  water,  and  then 
to  calculate  the  percentage  of  the  possible  amount  of  oxygen  present 
in  the  palluted  water  directly  from  the  amounts  of  thiosulphate 
which  equal  volumes  of  the  two  samples  require.  The  manganous 
chloride  must  be  free  from  iron,  and  all  the  reagents  must  be  free 
from  nitrites. 

It   has  been    objected    that    iodometric   methods    are    inapplic- 
able   to    waters    containing    much   organic    matter,   as    this   ma}' 
absorb   iodine — but    this   objection   does   not   appear    to  be  well 
founded. 


GASES  IN   WATER  65 

Ordinary  tap  water  at  room  temperature  contains  about  7  c.c.  O 
dissolved  per  litre,  or  by  weight  about  i  part  per  100,000. 

2MnCl2  +  4KOH  -  4KCI  f  2Mn(0H),. 
2Mn(OH)2  +  H20  +  0=2Mn(OH)3. 
2Mn(0H)3  +  6HC1=  2MnCl3  +  6H2O. 
2MnCL  +  2KI  =  2MnC]o  +  2KCI  +  L. 


CO2  in  Water. 

Carbon  dioxide  may  exist  in  solution  in  water  in  the  free  state, 
as  a  bicarbonate,  or  as  a  carbonate. 

Estimation  of  Total  CO2  (free  CO2,  CO2  in  bicarbonates,  CO2  in 
carbonates). — Solutions  and  apparatus  required: 

BaCl2  solution,  10  per  cent.  H2SO4,  baryta- water,  flask  of  capacity 
about  300  c.c,  fitted  with  a  perforated  bung  through  which  three 
holes  are  bored,  the  first  carrying  a  funnel  tube  provided  with  a 
stopcock,  to  hold  H2SO4 ;  the  second  carrying  a  glass  tube  almost  to 
the  bottom  of  the  flask,  and  connected  outside  to  a  bottle  containing 
baryta-water;  and  the  third  carrying  a  glass  tube  connected  with  a 
CaClg  tube  and  a  weighed  potash  bulb  containing  50  per  cent, 
solution  of  KOH. 

Process. — Measure  into  the  flask  200  c.c.  of  the  water  to  be 
examined,  and  50  c.c.  baryta- water,  together  with  5  c.c.  BaClg. 
Shake,  and  allow  to  settle  for  twenty-four  hours.  Decant  off  as 
much  of  the  clear  fluid  as  possible  without  disturbing  the  sediment. 
Should  there  be  a  scum  on  the  surface,  rapidly  run  the  fluid  through 
a  filter-paper,  and  drop  the  filter  into  the  flask.  Replace  the  bung 
and  run  in  slowly  the  H2SO4,  which  decomposes  the  carbonates. 
The  Ba(0H)2  has  previously  precipitated  as  carbonates  all  the 
free  COg  and  that  existing  as  bicarbonate.  The  total  COo  evolved 
by  the  action  of  H2SO4  is  absorbed  by  the  KOH  in  the  bulb.  \^'eigh 
the  bulb,  and  difference  in  weight  represents  this  COo. 

When  during  the  experiment  the  CO,  ceases  to  come  off,  the 
flask  should  be  gently  heated  in  order  to  assist  the  evolution,  and 
air  drawn  through  in  order  that  all  the  CO2  may  reach  the  KOH. 

Estimation  of  Free  CO2. — Measure  into  a  porcelain  basin 
100  c.c.  of  the  water;  add  a  few  drops  of  phenolphthalein,  and  run 
in  from  a  burette  a  solution  of  ^^  NagCOg  until  a  faint  red  colour  is 


66  PRACTICAL  SAXTTARY  SCIENCE 

developed.  The  sodium  carbonate  forms  %vith  tlie  CO,  sodium 
bicarbonate  (NaHCO.,),  and  immediately  all  the  CCX  is  used  up 
further  carbonate  turns  the  indicator  red.  The  amount  of  NaoCO., 
used  measures  the  quantity  of  COo  present. 

Na.,CO.j  +  CO.  +  H.,0=  2XaHC03. 

io6  grammes  Xa-^CO^  neutralize  44  grammes  CO,. 

(^  NagCOg  contains  per  c.c.  0-00265  gramme.) 

I  c.c.  of  the  sodium  carbonate  therefore  neutralizes  j^^j^  x  0-00265 
gramme  C02=  o-ooii  gramme  COo. 

If  in  an  estimation  it  is  found  that  3  c.c.  -j^  NagCOg  are  required 
to  neutrahze  the  CO.,  in  100  c.c.  water,  the  amount  of  CO.,  in  this 
water  will  be  3  x  o-ooii  gramme  =  0-003  gramme  =  3  milligrammes^ 
3  parts  per  100,000. 

Estimation  of  Free  COo  and  CO.  as  Bicarbonate.  —  If  to 
100  c.c.  of  the  water  a  little  BaCl.  be  added  to  precipitate  carbonates, 
sulphates,  and  phosphates  of  any  alkalies  which  might  be  present, 
and  which  would  precipitate  barium  from  baryta-water;  and, 
further,  if  a  little  saturated  ammonium  chloride  be  added  to  prevent 
the  precipitation  of  magnesia  (IMgCOg  would  precipitate  BaCO., 
from  Ba(0H)2),  the  CO.  existing  free  and  as  bicarbonate  ma}^  be 
neutraUzed  by  excess  of  Ba(0H)2;  ^^id  the  loss  in  alkalinity  of  the 
measured  excess  of  Ba(0H)2  solution  used  may  be  estimated  by 
titration  with  standard  oxalic  acid  (as  carried  out  in  Pettenkofer's 
method  of  estimating  CO.  in  the  air,  cf.  p.  133),  and  converted  into 
terms  of  CO2. 

The  CO2  due  to  bicarbonates  is  equal  to  the  figure  found  for  this 
estimation  less  that  for  free  CO2. 

Estimation  of  CO.  as  Carbonates  and  Bicarbonates. — To 
100  c.c.  of  the  water  add  a  few  drops  of  phenolphthalein,  which 
immediately  becomes  red  from  the  action  of  the  carbonates 
(phenolphthalein  remains  colourless  in  the  presence  of  bicarbonates). 
Run  in  standard  oxalic  acid,  i  c.c.=  i  milligramme  COg,  until  the 
indicator  loses  colour.     This  measures  the  carbonates. 

Now  boil  the  water  for  fifteen  minutes,  and  run  in  further  standard 
oxalic  acid  until  the  phenolphthalein,  which  in  the  meantime  has 
become  coloured,  again  becomes  colourless. 

The  first  addition  of  acid  converts  the  carbonates  into  bi- 
carbonates: hence  colourless  phenolphthalein. 


WATER  SEDIMENT  67 

Boiling  converts  the  bicarbonatcs  (original  and  converted)  into 
carbonates:  hence  red  phenolphthalein. 

The  second  addition  of  acid  measures  the  CO2  after  boiling. 
Twice  this  figure  represents  the  COg  as  bicarbonatcs  (original  and 
converted)  before  boiling.  If  from  this  last  figure  be  subtracted 
the  first  figure  found — ^viz.,  the  CO,  as  carbonates — the  remainder 
is  the  amount  of  COg  as  original  bicarbonatcs. 

One  hundred  c.c.  of  a  water  required  3  c.c.  oxalic  acid,  which 
means  that  it  contains  3  parts  CO2,  as  carbonates,  per  100,000. 
When  boiled  and  titrated  further  4  c.c.  of  acid  were  required. 
Total  bicarbonatcs  therefore  equal  4x2=8  milligrammes.  Lastly, 
8-3  =  5;  therefore  the  original  bicarbonatcs  in  the  water  amounted 
to  5  parts  per  100,000. 

Or  these  estimations  may  be  carried  out  without  heat  by  titrating 
with  a  standard  acid  and  two  indicators — phenolphthalein  and 
methyl  orange.  When  the  phenolphthalein  has  become  colourless 
(end  of  carbonates  estimation)  methyl  orange  is  added,  and  addition 
of  acid  continued  until  the  indicator  proclaims  the  presence  of  free 
acid  (end  of  bicarbonatcs  estimation).  Methyl  orange  is  sensitive 
to  bicarbonatcs. 

Sulphuretted  hydrogen  in  water  may  be  estimated,  by  titrating 
a  measured  quantity  with  -^  I. 

I2  +  H2S=2HI  +  S. 

A  drop  or  two  of  boiled  starch  solution  is  used  to  fix  the  end-point. 

[i  c.c.  J^  1  =  0-34  niilhgramme  HgS.] 


WATER  SEDIMENT. 

The  biological  examination  of  a  water  sediment  may  throw  much 
light  on  the  problem  of  its  origin  and  the  nature  and  mode  of  its 
contamination.  A  |-inch  and  ^-inch  objective  of  the  ordinar}^ 
English  microscopes  furnish  good  fields  for  this  work.  The  number 
of  possible  organic  forms — animal  and  vegetable- — that  may  con- 
taminate a  water  is  so  great  that  no  expert  could  be  expected  to 
recognise  all.  But  in  the  search  for  sewage  pollution  a  number  of 
unmistakable  objects  may  be  seen  that  will  clinch  the  diagnosis. 
The  micro-chemical  examination  of  mineral  particles,  such  as  iron 


68  PRACTICAL  SAXITARY  SCIEXCE 

compounds,  carbonates,  oxalates,  etc.,  is  in  certain  cases  of  some 
import;  but  the  investigation  of  animal  and  vegetable  matter  is 
much  more  likely  to  lead  to  positive  evidence  of  sewage  and  other 
organic  forms  of  pollution. 

In  this  chapter  a  few,  and  only  a  few,  general  remarks  will  be 
made  on  the  biological  examination,  and  the  student  will  do  well  to 
consult  such  works  as  Cooke's  *  British  Desmids,'  '  Fresh-water 
Algae,'  by  the  same  author,  Whipple's  '  Microscopy  of  Drinking 
Water,'  and  other  writers  on  the  Infusoria,  Rotifera,  Fungi,  etc. 
A  necessarily  limited  number  of  illustrations  are  given,  but  it  is 
hoped  that  these  will  be  sufficient  to  introduce  the  beginner  to  the 
microscopic  study  of  water  sediments,  which  in  every  examination 
should  be  faithfully  carried  out. 

Much  has  been  written  on  methods  of  procuring  the  sediment. 
Where  a  centrifugal  machine  is  at  hand  it  is  most  satisfactory  to 
use  it,  and  where  none  can  be  had  the  ordinary  conical  urine  glass 
suffices  in  ever}'  respect.  In  using  the  latter,  the  water  should 
stand  overnight.  The  clear  fluid  is  carefully  syphoned  or  poured 
awav,  and  the  sediment  at  the  bottom  is  removed  by  a  fine  pipette, 
and  dropped  in  single  drops  on  a  series  of  microscopic  slides.  Some 
workers  use  well-slides.  Should  there  be  a  scum  on  the  surface  of 
the  water  in  the  conical  glass,  this  is  removed  separately  and  trans- 
ferred in  like  manner  to  slides.  Cover-glasses  are  applied,  and  the 
slides  carefully  examined,  first  by  the  low  and  afterwards  b}-  the 
higher  objective. 

Certain  biological  forms  inhabit  only  foul  water,  and  disappear 
when  it  becomes  purified.  Where  a  supph'  usuall}'  satisfactory 
develops  colour,  turbidity,  or  odour,  a  microscopical  examination 
alone  mav  elucidate  the  causes.  A  satisfactory  water  should  be 
free  from  all  suspended  matter,  and  especially  from  all  living  and 
dead  animal  and  vegetable  matter.  Certain  animal  and  vegetable 
growths  may  occur  in  storage  reservoirs  and  cisterns  through  the 
admission  of  light  to  the  water:  plants  containing  chlorophyll  (green 
algae,  diatoms,  etc.)  grow  in  light.  The  different  seasons  bear 
different  forms  and  amounts  of  animal  and  vegetable  life,  therefore 
a  systematic  microscopical  examination  is  necessary.  Vegetable 
growths  may  take  place  at  dead  ends  in  mains.  Much  dead  organic 
tnatter  will  be  found  in  the  form  of  unrecognisable  debris,  but 


WATER  SEDIMENT 


fjrj 


Fig.  5. 


I. 

Wood  cells. 

6. 

Particles  of  sand. 

2. 

Cotton  fibre. 

7- 

Paramoecium. 

3- 

Linen  fibre. 

8. 

Amoeba. 

4- 

Hemp  fibre. 

9. 

Encysted  Infusorian 

5- 

Algal  zoospore. 

10. 

Algal  zoospore. 

Fig.  6. 

1.  Fresh-water  Hydra. 

2.  Scale  of  insect. 

3.  Egg  of  Taenia  solium. 

4.  Egg  of  Trichocephalus  dispar. 

5.  Egg  of  Ascarus  lumbricoides. 


6.  Paramoecium. 

7.  Amoeba. 

8.  Wool  fibre. 

9.  Euplotes  Charon. 
10.  Diatoms. 


PRACTICAL  SAXITARY  SCIEXCE 


1.  Pleurococcus  (Algae). 

2.  Amoeba  (Protozoa). 

3.  An  Infusorian. 

4  and  5.  Diatoms  (Algae). 
6.  A  Desmid  (Algae). 


Fig.  7. 


7.  Hair  of  insect. 

8.  Vegetable  tissue. 

9.  Fibre  of  wool. 
10.  Ulothrix  (Algae) 


Fig 


1.  Anguillulae  (Xematoda) 

2.  Ulothrix. 

3.  Zoogloea  of  micrococci. 

4.  Anabena. 

5.  Cryptomonas. 


6.  Chara  fragilis. 

7.  Diatom  (Synedra). 

8.  Uroglena. 

9.  A  Desmid  (Cosmarium). 
10.  Encysted  Infusorian. 


WATER  SEDIMENT 


71 


1.  Vorticella. 

2.  Spirogeira. 

3.  Sphgerotilus  natans. 

4.  Beggiatoa. 

5.  Daphnia. 


Fig.  9. 


6.  Crenothrix  polyspora. 

7.  Volvox  globator. 

8.  Tabellaria. 

9.  Species  of  NostocJ 
10.  Melosira. 


Fig.  10. 


1.  Rotifer  (Annuloida) . 

2.  Paramoecium  (Protozoa). 

3.  Animal  spine. 

4.  Wing  scale  of  an  insect. 

5.  Vegetable  debris. 


6.  Crystals  of  calcium  sulphate. 

7.  Algal  filaments. 

8.  Not  identified. 
g.  Bacteria. 

10.  Diatom. 


72  PRACTICAL  SAX  IT  A  RY  SCIENCE 

amongst  it  much  that  is  recognisable,  as  epithelium,  striped  muscle, 
cotton,  silk,  and  linen  fibres,  starch  granules,  dotted  vegetable  ducts, 
wool,,  hair,  ova  of  intestinal  worms,  and  numerous  other  bodies,  all 
distinctive  of  sewage.  It  will  thus  be  seen  that  a  knowledge  of  the 
fauna  and  flora  of  water  will  enable  workers  to  recognise  certain 
organisms,  alive  or  dead,  which  produce  odours  in  water,  others 
which  live  only  in  pure  waters,  and  whose  presence  excludes  gross 
pollution,  and  those  which  live  in  polluted  waters,  and  consequently 
point  to  sewage  or  other  contamination.     Fislw  odours,  according 


Fig.  II. 


1.  Oscillatoria. 

2.  Small  Infusorian. 

3.  Free-swimming  Vorticella. 

4.  Cotton  fibres. 

5.  Navicula  (Diatom). 

6.  Confervoid  Alga  (Synura  uvella). 


7.  A  Heliozoon. 

8.  Egg  of  an  Entozoon. 

9.  Pith  cells  partially  covered  with 

vegetable  debris, 
[o.  Wood  of  a  Conifer. 


to  Whipple,  are  produced  by  Endorina,  Volvox,  Pandorina,  and 
other  Chlorophyceae,  Uroglena,  Bursaria,  and  other  Protozoa. 
Aromatic  odours  are  created  by  numerous  diatoms — Tabellaria, 
Meridion,  Diatoma,  etc. — and  Protozoa.  Grassy  odours  are  pro- 
duced by  Rivularia,  Anabsena,  Cselosphaerium,  and  other  Cyano- 
phycese. 


WATER  SEDIMENT 


73 


In  river  water  and  unfiltered  supplies  possessing  odours  the 
organisms  are  likely  to  be  found  in  the  supply;  whilst  in  filtered 
waters  they  mostly  grow  on  the  filters.  The  foul  odour  and  reddish 
colour  of  the  Cheltenham  water  some  years  ago  was  shown  to  be 
due  to  a  species  of  Crenothrix  growing  in  the  reservoirs  and  on  the 
filters.  In  deep-well  and  spring  waters  any  low  forms,  animal  or 
vegetable,  indicate  insufficient  protection  from  light,  such  as  storage 
in  uncovered  reservoirs.  The  so-called  sewage  fungus,  Beggiatoa 
alba,  including  Carchesium  Lachmanni,  and  other  forms,  occurs  in 


Fig.  12. 


Leptomitus  lacteus  (from  impure 

river) . 
Carchesium      Lachmanni      (from 

water  polluted  with  sewage) . 
Conferva  bombycina(pond  water) . 
Fresh- water  Alga  (Lyngyba). 
Bursaria  gastris. 


6.  Hydrodictyon  (fresh-water  Alga) 

7.  Sand  particles. 

8.  Algal  lilament. 

9.  Hypha  of  fungus  (sporing). 

10.  Encysted  Protozoon. 

11.  Water  bear. 


effluents  from  sewage-farms  and  bacteria-beds.  Beggiatoa  also 
occurs  in  river  beds  and  stagnant  waters  containing  H.2S.  Wino- 
gradsky  holds  that  it  does  not  produce  the  S  which  it  contains  in  the 
dried  state,  but  that  this  S  is  derived  from  the  HgS  by  other  means. 
Cohn  states  that  it  produces  S  from  sulphates  and  albuminous  bodies. 
The  organisms  forming  the  slimy  superficial  layer  (Schlammdecke) 


74 


PRACTICAL  SAXITARY  SCIEXCE 


Fig.  13. — -Beggiatoa  Alba. 


I'lG.  14. — Daphxia  Pulex. 


WATER   SEDIMENT 


75 


Fig.    15. — ^VORTICELLA. 


Motile.  Resting. 

Fig.  16. — Amceba  Coli. 


76 


PRACTICAL  SAXITARY  SCIEXCE 


Fig.  17. — Leicestershire  Wool. 


Fig.  iS. — Chinese  Silk. 


WATER  SEDIMENT 


77 


Fig.  19. — Flax  Fibres. 


%!■  4 


Fig.  20. — Hemp  Fibres. 


78 


PRACTICAL  SAXITARY  SCIEXCE 


Fig.  21. — Jute  Fibres. 


A/ 


Fig.  22. — Cotton  Fibres. 


INTERPRETATION  OF  RESULTS  79 

of  a  sand-filter  are  innumerable,  and  vary  with  the  source  of  the 
water  and  other  factors. 

When  a  sand-filter  is  first  set  to  work,  it  acts  merely  as  a  strainer. 
In  the  course  of  a  few  days  a  slimy  organic  layer  consisting  of  green 
and  blue  algce,  fungi,  zoogloea  masses  of  bacteria,  diatoms,  and  a 
multitude  of  other  organisms,  makes  its  appearance,  and  true  filtra- 
tion then  commences.  The  source  of  the  water,  season  of  the  year, 
etc.,  determine  the  presence  of  specific  forms.  Certain  green  algse 
are  produced  in  the  spring,  blue  algae  in  the  summer,  and  their 
colouring  matter  may  be  liberated  at  any  time  and  remain  on  the 
surface  long  after  the  organisms  have  died. 

The  matter  obtained  as  sediment  from  a  centrifugal  machine, 
conical  glass,  or  surface  scum,  when  examined  microscopically,  may 
be  found  to  contain  (i)  living  animal  forms,  (2)  dead  animal  forms, 
(3)  living  vegetable  forms,  (4)  dead  vegetable  forms,  {5)  mineral 
detritus,  and  (6)  unrecognisable  debris,  requiring  micro-chemical  and 
other  methods  of  investigation. 

The  differentiation  of  some  lowly  animal  and  vegetable  organisms 
is  frequently  a  matter  of  no  little  difficulty,  but  careful  search  should 
be  made  for  these,  as  their  presence  has  special  significance. 


INTERPRETATION  OF  RESULTS  OF  CHEMICAL  ANALYSES. 

As  previously  indicated,  judgment  should  be  exercised  at  all  times 
in  expressing  an  opinion  on  a  water  without  a  personal  inspection 
of  the  source,  etc. ;  but  many  instances  will  arise  in  which  no  doubt 
can  exist  as  to  the  foulness  of  the  sample.  Positive  results  in  the 
search  for  sewage  contamination  are  much  more  easily  dealt  with 
than  negative.  The  liability  to  such  pollution  should  ever  be  kept 
before  the  mind  of  the  analyst.  Deep  springs  and  wells  for  the 
most  part  afford  the  purest  waters.  Upland  surface  waters  may  be 
also  quite  pure.  But  subsoil  waters  and  waters  from  cultivated 
lands,  as  also  most  river  waters,  are  rarely  free  from  pollution. 
Waters  collected  from  the  surfaces  of  the  more  impervious  rocks 
destitute  of  animal  and  vegetable  life,  are  extremely  pure.  These 
rarely  contain  any  appreciable  NH3,  and  rarely  more  than  i  part 
chlorine,  o-i  part  nitric  N,  5  parts  hardness,  and  10  parts  total 


8o  PRACTICAL  SAXITARY  SCIENCE 

solids  per  100,000.  Waters  collected  from  rocks  covered  with  peat 
will  present  high  figures  for  organic  ammonia,  and  O  absorbed  by 
organic  matter,  and  their  acidity  will  be  great.  Such  waters  are 
plumbo-solvent,  and  should  be  neutralized  before  distribution  to 
the  consumer.  Waters  from  mountain  limestone  are  moderately 
hard,  with  high  total  solids  and  neutral  or  faint  alkaline  reaction. 
The  mineral  residue  is  chiefly  composed  of  carbonate  and  sulphate 
of  calcium  and  magnesium.  Great  variety  in  composition  is  found 
amongst  waters  originating  in  the  lias,  magnesium  limestone,  red 
sandstone,  and  oolite;  total  solids  may  range  from  10  to  15  parts; 
total  hardness  10  to  15;  chlorine  i  to  2;  and  nitric  N  o-i  to  0-2. 
Alluvial  strata  furnish  waters  of  high  total  solids  (50  to  100) ;  and 
waters  from  cultivated  soils  vary  within  very  wide  limits  in  total 
solids,  hardness,  chlorine,  and  nitric  N. 

Hard  waters  are  derived  from  the  chalk,  limestone,  magnesian 
limestone,  oolite,  and  dolomite. 

Chalk  waters  are  mostty  bright,  transparent,  and  charged  with 
CO.2.  \Mien  the  CO2  is  driven  off,  these  waters  are  almost  univer- 
sally alkaline,  although  before  boiling  the  reaction  to  litmus  may  be 
distinctly  acid.  Chlorine  varies  from  2  to  3  parts,  nitric  nitrogen 
from  0-2  to  0-4,  total  hardness  15  to  30  (the  hardness  is  chiefly  tem- 
porar}^  and  may  be  nearly  all  due  to  carbonates  of  Ca),  and  total 
solids  from  25  to  50  parts. 

Waters  from  oolite  closely  resemble  those  from  chalk,  with  the 
exception  that  they  contain  a  little  more  permanent  hardness. 
Limestone  waters  contain  more  total  solids  and  more  permanent 
hardness  (due  principally  to  calcium  and  magnesium  sulphate). 
Waters  from  dolomite  strata  occupy  an  intermediate  position  be- 
tween chalk  and  limestone  waters  in  point  of  hardness  and  total 
solids.  Greensands,  in  that  they  frequently  contain  much  nitrates 
and  variable  quantities  of  ferrous  iron,  furnish,  through  the  reduction 
of  the  nitrates  bj'  the  iron,  quantities  of  free  NH3.  The  intermediate 
stage  of  nitrites  ma\^  be  occasionally  demonstrated.  The  lower 
greensand  furnishes  water  collected  at  great  depth — often  many  feet 
below  the  chalk — and  accordingly  the  total  soJids  are  high,  often  80 
to  100  parts  per  100,000.  Hardness  is  very  variable,  and  much  is 
permanent.  Chlorine  may  run  to  10  or  12  parts  per  100,000,  and 
nitric  X  to  as  much  as  0-5  or  o-6.     These  waters  are  very  free  from 


INTERPRETATION  OF  RESULTS  8i 

organic  matter.  Where  water  is  procured  from  lias  clays  much 
permanent  hardness  may  be  expected  (CaS04  and  MgvSO^),  20  parts 
or  more,  and  total  solids  may  range  from  200  to  300. 

A  water  containing  over  30  parts  of  total  hardness  may  be  con- 
sidered unsuitable  for  domestic  purposes,  unless  it  can  be  largely 
softened. 

Waters  containing  more  than  20  parts  of  permanent  hardness  are 
not  suitable  for  washing  and  cooking. 

Deep  wells,  if  sufficiently  steined,  are  for  the  most  part  pure. 
Very  occasionally  a  well  in  the  chalk  may  tap  a  hidden  reservoir 
of  unpurilied  sewage  which  has  leaked  through  fissures  from  a  cess- 
pool. 

Sewage  derives  the  bulk  of  its  CI  from  urine,  which  contains,  as 
above  mentioned,  about  i  per  cent,  chlorides,  but  although  it  con- 
tains this  large  amount  of  CI,  it  is  obvious  that  deadly  pollution  by 
sewage  may  occur  in  such  small  amounts  as  are  wholly  incapable  of 
detection  by  chemical  methods ;  the  chlorine  figure,  therefore,  will  be 
chiefly  of  diagnostic  value  in  those  cases  where  the  soil,  subsoil,  and 
water-bearing  strata  are  of  constant  composition  and  beyond  the 
reach  of  contamination  by  cultivated  land.  If  after  a  series  of 
analyses  the  CI  figure  is  found  fairly  constant,  a  particular  rise  of 
0*5  to  I  part  per  100,000  may  justly  arouse  a  suspicion  of  sewage 
pollution. 

Considering  the  varieties  in  source  and  surrounding  conditions 
from  source  to  distribution,  it  is  quite  impossible  to  erect  standards 
of  purity  for  waters  in  this  country.  An  inspection  of  the  source 
and  surroundings  is  of  the  utmost  importance  in  all  cases. 

In  considering  the  '  free  and  saline  '  NH3,  the  merest  trace  should 
be  considered  of  import  if  not  suspicious,  except  in  those  cases  where 
reduction  of  nitrates  has  taken  place,  such  as  occurs  in  the  green- 
sands.  As  previously  stated,  if  the  '  albuminoid  '  ammonia  be  very 
small  (less  than  0-002),  the  '  free  and  saline  '  may  be  allowed  to 
exceed  slightly  0-005.  In  peaty  waters,  where  the  '  albuminoid  ' 
ammonia  may  reach  o-oi,  the  '  free  and  saline  '  should  be  negligible. 
In  a  deep-well  water  the  O  absorbed  from  permanganate  in  3  hours 
at  37°  C.  should  not  exceed  o-oi  or  0-02.  In  a  peaty  water  free 
from  animal  pollution  this  figure  may  exceed  0  -i . 

In  passing  judgment  on  river  waters,  analyses,  in  addition  to 

6 


S2  PRACTICAL  SAX  IT  A  RY  SCIENCE 

inspection,  should  be  made  of  all  tributaries,  lest  evidence  of  present 
or  past  pollution  be  overlooked.  The  search  for  poisonous  metals 
should"  be  carefully  carried  out,  and  when  any  of  these  is  found  a 
quantitative  estimation  should  in\-ariably  be  made.  Lead  to  the 
extent  of  0-025  P'^rt  per  100,000  is  sufticient  to  condemn  a  potable 
water.  Present  or  recent  sewage  pollution  may  be  mt)re  or  less 
accuratel}'  differentiated  from  past  and  remote,  in  that,  whilst 
high  CI  and  nitrate  ligures  obtain  in  both,  in  the  present  or 
recent  contamination  there  will  be  marked  free  and  organic  XH3, 
whereas  in  the  past  and  remote  little  or  no  free  or  organic  NH3 
will  be  found.  Further  animal  pollution  may  be  more  or  less 
accurately  differentiated  from  vegetable  by  contrasting  the  two 
ammonias,  oxygen  absorbed  b}'  Tidy's  process,  CI,  and  nitrates. 
All  these  figures  are  high  in  cases  of  marked  animal  pollution; 
whilst  in  A-egetable  pollution  free  NH3  is  low,  organic  NH3  high, 
CI  and  nitrates  are  low,  and  in  the  last  two  no  increase  if  the 
water  is  drawn  from  below  the  surface.  Where  much  vegetable 
matter  exists  the  water  is  usually  coloured,  as  in  the  various  peaty 
waters,  and  the  solid  residue  chars  on  ignition.  Sulphates  and 
phosphates  occur  in  larger  quantities  in  water  polluted  with 
animal  matter  than  in  those  contaminated  with  \-egctable  material. 
Little  has  been  said  of  nitrites,  because,  although  the}^  are  easily 
foimed  by  oxidizing  and  reducing  agents,  they  are  rarely  present 
in  natural  waters.  They  are  found  in  purifying  sewage,  but, 
unfortunately,  as  they  may  be  formed  from  other  sources  than 
ammonia  (such,  e.g.,  as  nitrates  in  contact  with  iron,  zinc,  and  lead 
pipes  or  cisterns),  it  is  not  alwaj^s  possible  to  locate  their  origin. 
The  faintest  trace,  however,  of  nitrites  should  condemn  a  water, 
except  in  the  single  instance  of  a  pure  water  containing  nitrites 
undergoing  reduction  b}^  metallic  or  other  inorganic  compounds, 
and  not  by  organic  matter. 

The  solids  impart  different  properties  to  waters  according 
to  their  composition,  so  that  no  strict  limit  can  be  set  to  their 
amount.  Sulphates  should  not  exist  in  larger  quantity  than 
S  parts  SO2  per  100,000.  Magnesium  salts,  especially  MgSOj, 
should  be  very  small,  if  at  all  present,  in  a  good  water.  And  per- 
haps, all  forms  of  mineral  matter  considered,  the  total  figure  should 
not  nearly  reach  100. 


CHAPTER  VII 
THE  BACTERIOLOGY  OF  WATER 

The  student  who  works  with  a  microscope  should  be  familiar  with 
the  elementary  mathematics  of  the  instrument ;  he  should  understand 
the  principles  which  underlie  the  formation,  magnification,  and 
brightness  of  images.  The  following  matters  require  special  atten- 
tion: (i)  The  conditions  which  produce  an  aplanatic  image  as 
expressed  in  Abbe's  sine  law — in  other  words,  the  conditions  which  ex- 
clude spherical  aberration  and  coma.  (2)  The  angular  and  numerical 
aperture  of  a  lens  and  their  relations  to  the  refractive  indices  of 
glass,  air,  cedar-wood  oil,  etc.  (3)  The  meaning  of  resolution  as 
applied  to  lenses  and  the  factors  determining  its  limits.  (4)  The 
definition  of  lenses.  (5)  Methods  of  excluding  chromatic  aberration. 
(6)  The  flatness  of  images.  (7)  The  theory  of  the  Huygenian  eye- 
piece, (8)  Methods  of  illumination  including  oblique  or  dark  ground 
illumination.  (9)  The  simple  relations  between  objectives  (high 
and  low  power),  Abbe  condenser,  mirror  (plane  and  concave), 
diaphragm,  and  source  of  light. 

The  student  approaching  the  bacteriology  of  water  is  assumed  to 
have  a  good  bench  knowledge  of — 

1.  The  preparation  and  examination  of  the  hanging  drop  with  a 
view  to  determination  of  motility,  immotility,  and  Brownian  move- 
ment. 

2.  The  preparation  and  staining  by  a  simple  stain  of  a  smear  or 
section  with  the  object  of  discovering  the  morphology  of  the  micro- 
organism or  micro-organisms  under  examination — coccus,  bacillus, 
vibrio. 

3.  The  preparation  of  a  Gram  specimen.  He  ought  to  be  able  to 
definitely  state  whether  his  specimen  is  positive  or  negative. 

4.  The  few  special  stains — (?.g.,  Ziehl  Neelsen's,  used  for  Bacillus 

83 


84  PRACTICAL  SANITARY  SCIENCE 

iiiberciilosis  and  acid-fast  bacteria;  Neisser's,  used  for  the  Klebs- 
Loffler  bacillus,  etc. 

5.  The  preparation  of  and  results  obtained  by  the  various  fermen- 
tation media  in  common  use,  especially  those  for  intestinal  bacteria. 

6.  The  methods  employed  in  carrying  out  immunity  reactions 
between  micro-organisms  and  blood  serum. 

The  bacteriological  examination  of  water  as  a  routine  procedure 
seeks  (i)  to  measure  the  extent  to  which  it  has  been  polluted  b}^ 
sewage;  or  (2)  to  determine  the  degree  of  completeness  of  purifica- 
tion processes;  or  (3)  to  detect  the  presence  of  definite  disease- 
producing  organisms,  such  as  B.  typhosus,  etc.  Since  the  number 
of  definite  pathogenic  organisms  compared  with  the  total  number  of 
bacteria  in  water  is  very  small,  and  since  competition  may  have 
wholly  eliminated  the  disease-producers  by  the  time  the  water 
reaches  the  laboratory,  the  search  under  head  (3)  becomes  so  un- 
satisfactory that  it  is  but  rarely  attempted.  The  search  under 
head  (2)  is  most  serviceable  in  determining  the  efficiency  of  sedi- 
mentation and  filtration  of  large  quantities  of  water.  The  micro- 
organisms characteristic  of  sewage  generally  styled  '  indicator  ' 
organisms — viz.,  B.  coli,  streptococci,  and  B.  enteritidis  sporogenes — 
when  estimated  quantitatively  determine  with  considerable  accuracy 
the  degree  of  sewage  pollution  remaining  at  any  stage  in  the  puri- 
fication of  a  water-supply,  and  to  the  expert  in  charge  this  piece  of 
bacteriological  evidence  is  of  the  first  moment.  But  the  search  under 
head  (i)  is  that  most  widel3^  engaged  in. 

B.  Coli. 

Of  the  three  indicator  organisms  above  named,  B.  coli  is  by  far 
the  most  important ;  so  universally  is  this  recognised  that  the  bulk 
of  bacteriological  examinations  of  water  is  limited  to  a  quantitative 
determination  of  this  organism  alone.  We  have  in  the  B.  coli  group 
bacteria  extremely  numerous  in  excreta  and  sewage,  but  which  do 
not  occur  in  air,  soil,  or  water  unless  these  have  been  in  contact  with 
sewage. 

It  is  difficult  to  define  the  characters  of  the  group.  All  its 
members  are  non-sporing  short  bacilli.  Gram  negative,  motile, 
although  motility  is  not  always  seen,  fermenters  of  glucose  and 


THE  BACTERIOLOGY  OF  WATER  85 

lactose  with  production  of  acid  and  gas,  and  fail  to  liquify  gelatin 
in  fourteen  days.  Attempts  have  been  made  in  recent  years  to 
differentiate  the  strains  of  B.  colt  found  in  human  excreta  from 
those  of  the  domestic  and  other  animals.  At  present  it  is  impossible 
to  distinguish  B.  coli  isolated  from  water  as  belonging  to  any  species 
of  animal.  Whether  or  not  B.  coli  of  intestinal  origin  can  be  definitely 
separated  from  B.  coli  of  soil,  etc.,  is  a  matter  of  much  difference  of 
opinion.  The  broad  landmarks  that  separate  the  fermentation 
reactions  of  B.  coli  from  those  of  B.  typhosus  and  B.  enteritidis 
(Gartner)  necessarily  disappear  when  varieties  of  B.  coli  are  to  be 
distinguished.  Under  favourable  conditions  B.  coli  may  persist  for 
considerable  periods  outside  the  intestinal  tract  which  is  its  natural 
habitat;  but  under  ordinary  conditions  it  disappears  rapidly  from 
soil,  water,  etc.  This  last  statement  is  vindicated  by  the  self- 
purification  of  rivers  from  B.  coli  carried  into  them  by  sewage,  and 
by  experimentally  applying  sewage  to  soil,  water,  etc.,  and  determin- 
ing the  dates  at  which  B.  coli  can  no  longer  be  found.  Whether  it 
be  safe  to  rely  on  fine  distinctions  in  f ennentative  reactions  and  on 
pathogenic  and  agglutination  properties  as  means  for  separating 
B.  coli  of  recent  intestinal  origin — the  type  most  clearly  indicative 
of  danger — from  organisms  that  have  persisted  in  water,  soil,  etc., 
after  typhoid  bacilli  or  cholera  vibrios  have  perished,  is  a  question 
which  all  water  investigators  have  to  face,  and  until  it  can  be 
definitely  answered — and  that  time  is  not  yet — it  would  appear  to  be 
safer  to  regard  all  forms  of  B.  coli  as  possible  indicators  of  sewage. 
Houston  some  years  ago  worked  out  a  set  of  tests  represented  by  the 
symbol  '  flaginac '  to  assist  in  distinguishing  B.  coli  of  intestinal 
origin — viz.  : 

Greenish  fluorescence  in  neutral  red  broth  =  fl. 

Acid  and  gas  in  lactose  peptone  media  =  ag. 

Indol  in  broth  or  peptone  water  =  in. 

Acidity  and  clotting  in  litmus  milk  =  ac. 

Later  he  modified  his  procedure  somewhat  and  adopted  the  follow- 
ing three  tests  for  B.  coli,  using  in  each  case  portions  of  water  measur- 
ing 100  c.c,  TO  c.c,  I  c.c,  o-i  c.c,  o-oi  c.c,  and  o-ooi  c.c. : 

I.  Presumptive. — Gaseous  fermentation  of  a  bile  salt  glucose 
peptone  medium. 


86  PRACTICAL  SANITARY  SCIENCE 

2.  Confirmatory. — Isolation  of  a  coli-likc  microbe  forming  gas 
either  in  a  lactose  or  glucose  medium. 

3.  Typical. — Isolation  of  a  coli-like  organism  forming  indol  in 
peptone  water  and  gas  in  a  lactose  medium. 

Houston  was  the  first  to  use  the  above  and  lesser  dilutions  with 
the  object  of  placing  Public  Health  bacteriology  on  a  combined 
qualitative  and  quantitative  basis.  He  used  the  words  '  flaginac  ' 
and  '  typical  '  only  as  an  indication  that  specified  tests  have  been 
carried  out,  and  did  not  claim  that  '  flaginac  '  or  '  typical '  B.  coli 
are  onl}'  found  in  human  excremental  matter. 

Technique  of  the  Search  for  '  Flaginac  '  B.  Coli. — Remove  bottle 
of  water  for  examination  from  its  case  and  gently  shake  it.  Remove 
cork  and  flame  mouth.  Sow  100  c.c.  of  the  water  into  50  c.c. 
MacConkey's  fluid,  triple  strength,  in  a  Durham's  tube.  Sow  10  c.c. 
into  10  c.c.  MacConkey  double  strength-  Sow  i  c.c.  into  10  c.c. 
MacConke}'  ordinary  strength .  After  forty-eight  hours  incubation 
at  37°  C.  note  presence  or  absence  of  gas.  If  gas  is  found,  dilute  a 
loopful  of  the  culture  in  10  c.c.  sterile  water  and  spread  two  loopsful 
of  the  dilution  on  a  surface  culture  of  MacConkey's  tauro-chloate- 
lactose  agar  for  isolation.  Examine  after  forty-eight  hours  for  coli- 
like  colonies.  If  such  be  found  sow  one  or  two  in  a  tube  of  liquefied 
glucose-gelatin  and  incubate  at  20°  C.  If  gas  be  formed  liquefy  the 
gelatin  and  use  it  for  sowing  neutral  red  broth,  peptone  water,  and 
litmus  milk.  Examine  for  fluorescence,  indol,  and  acid,  and  clot 
respectively.  An  organism  giving  all  these  reactions  is  said  to  be 
'  flaginac  '  or  '  typical '  B.  coli. 

Streptococcus  Group. 

There  does  not  appear  to  be  any  uniform  classification  of  strepto- 
cocci. Morphology,  pigment  production,  agglutination  tests,  patho- 
genicity, and  production  of  acid  in  sugars  have  all  been  recommended 
as  bases  for  classification.  But  for  water  examination  attempts  to 
differentiate  isolated  streptococci  have  been  up  to  the  present  wholly 
unsuccessful. 

Technique  of  Search  for  Streptococci. — Sow  i  c.c.  of  the  water  into 
ID  c.c.  of  ordinary  broth.  Incubate  at  37°  C.  After  forty-eight 
hours  examine  the  deposit  microscopically  for  streptococci. 


THE  BACTERIOLOGY  OE  WAT  Eli  87 

B.  Enteritidis  Sporogenes  (Klein). 

This  bacillus  possesses  distinctive  characters.  It  is  fairly  large — 
2  to  4  //  long  by  o-8/^  broad;  it  is  motile;  it  spores  near  the  ends  of 
the  rods ;  it  is  Gram  positive ;  it  grows  anaerobically  in  milk,  producing 
a  characteristic  coagulum  of  casein  and  a  transparent  or  turbid  and 
acid  whey,  whilst  gas  is  formed  in  quantity.  The  contents  of  the 
incubated  milk  tube  smell  of  butyric  acid.  When  a  c.c.  of  the 
whey  containing  numbers  of  bacilli  is  injected  into  the  groin  of  a 
guinea-pig  the  animal  dies  within  twenty-four  hours,  and  post- 
mortem examination  reveals  an  extensive  gangrenous  slough  at  the 
seat  of  inoculation.  These  post-mortem  appearances,  together 
with  the  changes  in  the  milk,  identify  the  organism. 

As  B.  enteritidis  sporogenes  is  a  sporing  organism  with  prolonged 
powers  of  resistance  it  can  hardly  be  regarded  as  indicative  of  recent 
excretal  pollution.  Indeed,  opinion  is  far  from  united  concerning 
its  value  as  an  indicator  of  sewage  pollution. 

Technique  of  Search  for  B.  Enteritidis  Sporogenes.- — Sow  10  c.c.  of 
the  water  into  50  c.c.  of  milk,  taking  care  to  pass  the  pipette  well 
below  the  cream.  Sow  i  c.c.  into  10  c.c.  milk.  Heat  the  tubes  to 
80°  C.  for  fifteen  minutes,  and  then  incubate  in  an  anaerobic  appara- 
tus at  37°  C.  The  typical '  enteritidis  '  change  consists  in  formation 
of  gas,  odour  of  butyric  acid,  separation  of  curd,  and  tearing  of  same 
by  gas. 

It  is  impossible  to  set  up  rigid  bacterial  standards  for  waters. 
But  the  source  being  known  general  indications  can  readily  be  offered 
as  to  what  should  be  expected  of  a  good  water.  Since  the  more 
recent  the  excremental  pollution  the  greater  the  number  and  the 
older  the  pollution  the  less  the  number  of  B.  coli  present,  the  bacterio- 
logical potentialities  of  a  sewage-contaminated  water  would  appear 
to  be  best  expressed  in  terms  of  the  number  of  B.  coli  found. 

For  deep  wells  and  springs  a  more  restricted  standard  will  be 
demanded  than  for  shallow  wells,  rivers,  upland  surface  waters,  etc. 

For  deep  wells  and  springs  it  may  be  required  that  B.  coli  and 
streptococci  be  absent  from  100  c.c,  and  that  B.  enteritidis  spor- 
ogenes be  absent  from  a  litre ;  that  the  growth  on  gelatin  at  22  degrees 
does  not  exceed  fifty  organisms  per  c.c,  whilst  that  on  agar  at 
37  degrees  does  not  exceed  five  per  c.c 


88  PRACTICAL  SANITARY  SCIENCE 

In  shallow  wells,  rivers,  upland  surface  waters,  etc.,  this  standard 
may  be  relaxed  to  one-tenth — viz.,  absence  of  B.  coli  and  strepto- 
cocci from  10  c.c,  and  of  B.  enteritidis  sporogenes  from  lOO  c.c. ; 
gelatin  growth  not  to  exceed  500  per  c.c,  and  agar  not  more  than 
50  per  c.c. 

Sea  water  is  regarded  as  polluted  by  most  observers  when  it 
contains  B.  coli  in  i  c.c.  Houston  states  that  no  sample  of  sea 
water  remote  from  pollution  contains  B.  coli  or  spores  of  Enteritidis 
sporogenes  in  100  c.c.  Whilst  no  absolute  standards  can  be  fixed,  it 
may,  perhaps,  be  stated  in  a  general  way  that  samples  in  which 
B.  coli  is  present  in  10  c.c,  but  absent  in  i  c.c,  are  to  be  regarded 
as  suspicious. 

Techniqiie — Collection  of  Sample. — i .  A  white  glass  bottle,  capacity 
200-500  c.c,  is  sterilized  and  plugged  with  sterile  cotton-wool. 
2.  Before  filling  flame  the  mouth  and  remove  the  plug;  fill  quickly, 
and  insert  a  new  cork  which  has  just  been  passed  through  a  flame  till 
slightl}'  carbonized.  Cut  off  cork  level  with  mouth  and  seal  with 
wax.  Cover  with  a  rubber  cap.  In  taking  water  from  a  river, 
submerge  bottle  some  distance  from  bank  with  mouth  upstream; 
from  a  tap,  let  run  to  waste  before  filling;  from  well,  lower  under 
same  conditions  as  bucket  is  lowered,  or  fill  from  bucket,  or  use  a 
Miquel  flask. 

As  organisms  rapidly  multiply  in  water  at  ordinary  temperatures 
the  sample  should  be  kept  at  0°  C.  until  examination  is  commenced. 
Special  boxes  containing  ice  are  prepared  for  this  purpose. 

The  label  should  specify  (i)  Reasons  for  examination  (epidemic, 
etc.);  (2)  source  of  water;  (3)  particulars  concerning  recent  rains, 
snow,  pollution,  etc  ;  purposes  for  which  water  is  required  (drinking, 
cooking,  lavatories,  etc) ;  (4)  atmospheric  temperature;  (5)  day  and 
hour  of  collection. 

Enumeration  of  Organisms. — Prepare  a  few  10  c.c.  pipettes  plugged 
at  the  upper  end  with  wool,  and  sterilize  them ;  also  a  drop  pipette 
(20  drops  =  I  c.c). 

Sterilize  some  conical  flasks  plugged  with  wool.  Liquefy  a  few 
tubes  of  gelatin  in  a  water-bath,  and  prepare  some  sterile  distilled 
water. 

Measure  9  c.c.  sterile  water  into  a  flask,  taking  the  necessary 
precautions  to  avoid  all  contamination;  to  this  add  i  c.c.  of  the 


THE  BACTERIOLOGY  OF  WATER  89 

water  under  investigation,  and  mix.     The  mixture  is  a  dilution  of 
I  in  10. 

Flame  the  mouth  of  a  conical  flask;  remove  the  plug;  introduce 
with  the  drop  pipette  2  drops  of  the  i  in  10  dilution.  Flame  the 
mouth  of  a  gelatin  tube,  remove  the  plug,  and  quickly  pour  the 
contents  into  the  conical  flask;  mix,  and  stand  the  flask  on  a  cold 
horizontal  surface — ice  in  hot  weather. 

A  gelatin  plate  has  been  made  containing  o-oi  c.c.  of  the 
water. 

Incubate  this  at  20°  to  22°  C. 

Examine  the  flask  daily  for  appearance  of  colonies,  and  make 
counts  until  the  gelatin  is  completely  liquefied. 

Suppose  by  the  fifth  day  there  are  90  colonies,  and  on  the  sixth 
the  plate  is  completely  liquefied,  record  is  made  that  "  the  water 
contains  9,000  (100  x  90)  aerobic  micro-organisms  per  c.c,  liquefac- 
tion of  the  gelatin  having  finished  the  count  on  the  sixth  day." 

Enumeration  may  be  carried  out  with  pipettes  (made  in  France) 
which  deliver  about  50  drops  to  the  c.c.  The  exact  number  of  drops 
per  c.c.  is  marked  on  the  stem. 

In  the  same  manner  inoculate  melted  agar  at  40°  C.  and  pour 
plates;  incubate  at  37°  C.  for  three  days;  count. 

Qualitative  Examination. — Sow  i  drop  of  the  water  in  a  tube  of 
melted  gelatin  or  agar;  mix;  sow  2  loopfuls  of  the  mixture  into  a 
second  tube  of  gelatin  or  agar;  mix;  sow  2  loopfuls  of  the  last 
mixture  into  a  third  gelatin  or  agar  tube;  pour  plates  in  Petri  dishes 
with  these  mixtures.  The  plates  are  carefully  observed  daity,  and 
subcultures  sown  in  other  media  for  the  identification  of  a  particular 
colony.  Many  saprophytes  in  water,  although  incapable  of  causing 
infections,  may,  like  Proteus  vulgaris  and  Micrococcus  prodigiosus, 
produce  soluble  toxins  which  injuriously  affect  man  and  the  lower 
animals ;  others  may  cause  a  nuisance  bj^  producing  in  dead  organic 
matter  foul-smelling  gases. 

The  detection  of  pathogenic  species,  such  as  Bacillus  typhosus,  is 
generally  a  matter  of  some  labour.  When  the  student  has  gained 
facility  in  technique,  he  should  conscientiousl}^  work  out  the  various 
sugar  reactions,  growths  on  special  media,  and  the  tinctorial  and 
morphological  characters  of  this  and  a  few  other  pathogenic  fonns, 
such   as   B.    pyocyaneus,    Friedlander's   bacillus,    and   the   micro- 


90  PRACTICAL  SANITARY  SCIENCE 

organisms  of  suppuration.     Detailed  descriptions  of  methods  must 
be  sought  in  systematic  works  on  pathological  bacteriology- 

The  various  items  of  the  analysis  are  recorded  in  some  such  form 
as  this: 

Sample  of  water  from  — ■ — Date  

Labelled 

Brief  particulars  of  source — 

Physical  characters  : 

Turbidity 

Colour 

Odour 

Reaction - 


Free  and  saline  NH.^ parts  per  100,000. 

Albuminoid  NH3 '- - 

CI 

Nitrous  N 

Nitric  N 

Hardness  (total) ■■ 


(permanent)- 
(temporary)  _ 


O  absorbed  at  37°  C  in  three  hours. 
Metals 


Solids  (total). 


(volatile) - 
(fixed) ._ 


Appearance  on  ignition 

Microscopic  examination  of  sediment- 
Bacteriological  Examination  


WATERS  FROM   VARIOUS  SOURCES 


91 


EXAMPLES  OF  WATERS  FROM  VARIOUS  SOURCES 

Results  Expressed  as  Parts  per  ioo.ooo. 


No.  I. 
A  Pure  Water. 

No.  2. 

Rain  Water  Collected 

on  Grass  Land. 

Physical  characters     - 

_ 

Excellent 

Good 

Reaction    -         -         - 

- 

Faint  alkaline 

Faint  alkaline 

Free  and  saline  NH3  - 

- 

o-ooi 

0-012 

Organic  NH3 

- 

O'OOI 

Nil 

CI       -         -         -         - 

- 

I-20O 

0-200 

Nitrous  N            -         - 

- 

Nil 

Nil 

Nitric  N      -         -          - 

- 

O'OIO 

o-oio 

Hardness  (total) 

- 

8-500 

0-600 

(permanent) 

- 

3-000 

0-600 

(temporary) 

- 

5-500 

Nil 

0  absorbed  at  37°  C.  in  three  hours 

0'0i3 

0-002 

Metals  (Zn,  Pb,  Fe,  Cu) 

- 

Nil 

Nil 

Solids  (total) 

- 

ii'5oo 

2-500 

,,     (volatile)  - 

- 

2-500 

I-OOO 

„     (fixed)       - 

- 

g-ooo 

1-500 

Appearance  on  ignition 

- 

Nil 

Nil 

Microscopic  examination  of  sedi- 

ment      -         -         - 

- 

Nil 

Nil 

Bacteriological  examination 

20  non  -  liquefying 

Not  performed 

saprophytes     per 

c.c.         Intestinal 

organisms  absent 

No.  3. 
Foul. 

No.  4. 
Chalk  Water  from 

Deep  Well. 

Physical  characters  - 

_ 

Excellent 

Excellent 

Reaction     -         -         - 

- 

Alkaline 

Alkaline 

Free  and  saline  NH3  - 

0-030 

0-005 

Organic  NH3 

- 

O-02O 

0-006 

CI    -             -         -         - 

- 

5-000 

4-500 

Nitrous  N  - 

- 

0-050 

Nil 

Nitric  N      -         -         - 

- 

0-600 

0-300 

Hardness  (total) 

- 

20-000 

22-000 

(permanent) 

- 

12-000 

I2-000 

(temporary) 

- 

8-000 

lO-OOO 

0  absorbed  at  37°  in  three  hours 

0-150 

0-060 

Metals  (Zn,  Pb,  Fe,  Cu) 

- 

Nil 

Nil 

Solids  (total)      - 

- 

30-500 

38-000 

(volatile) 

- 

10-500 

I2-000 

,,       (fixed)      - 

- 

20-000 

26-000 

Appearance  on  ignition 

- 

Marked  charring 

charring 

Microscopic  examination  of  sedi- 

ment      -         -         - 

- 

Objects   indicating 
sewage  pollution 

Nil 

Bacteriological  examination 

B.    coli    found     in 

Not  performed 

50  c.c. 

92 


PRACTICAL  SANITARY  SCIENCE 


Sample  No.  2,  although  it  possesses  a  high  '  free  '  NH3  figure,  is 
good.  Rain  water  in  towns  is  general!)'  impure;  it  is  slightly  acid 
from  SO,,  and  contains  NHg. 

Sample  No.  3  has  had  a  small  amount  of  untreated  sewage 
admitted  to  it. 

Sample  No.  4  is  an  average  chalk  water  with  low  total  solids. 
This  figure  may  be  allowed  to  go  up  to  200  or  over.  The  hardness 
of  chalk  waters  varies  considerably. 

Sample  No.  5. — The  saline  NH3,  chlorine,  and  nitrates  are  high, 
and  nitrites  are  present.     These  items  in  general  point  to  animal 


No.  5. 

No.  6. 

Deep-well  Water  from 

Deep-well  Water  from 

the  Lower  Greensand. 

Chalk  near  the  Sea. 

Physical  characters    - 

- 

Good 

Saline   taste,   green- 
ish     colour,      no 
odour 

Reaction    -         -         - 

- 

Alkaline 

Alkaline 

Free  and  saline  XH3  - 

- 

0-035 

Nil 

Organic  XHo 

- 

o-ooi 

0-003 

CI       -         -         -         - 

- 

12*250 

115-000 

Nitrous  N  - 

- 

0-020 

Nil 

Nitric  N     - 

- 

0-320 

i-ooo 

Hardness  (total) 

- 

16-000 

47-000 

(permanent) 

- 

10-000 

— 

(temporary) 

- 

6-000 

— 

0  absorbed  at  37°  C.  in  three  hours 

0-020 

0-035 

Metals  (Zn,  Pb,  Fe,  Cu) 

- 

Nil 

Nil 

Sohds  (total) 

- 

105-000 

260-500 

(volatile) 

- 

20-000 

35-500 

„       (fixed)      - 

- 

85-000 

225-000 

Appearance  on  ignition 

- 

Nil 

Slight  darkening 

Microscopic  examination 

of  sedi- 

ment       .         -         - 

- 

Nil 

Mineral  particles 

Bacteriological  examination 

Excellent 

Excellent 

pollution;  that  they  are  not  due  to  this  cause  here  is  shown  b}'  the 
low  organic  XH3  and  0  absorbed.  Reduction  of  nitrates  by  iron 
salts  is  going  on,  as  demonstrated  b}'  the  high  saline  NH3  and 
presence  of  nitrites. 

Sample  No.  6  is  contaminated  by  sea  water.  Before  contamina- 
tion CI  was  3,  and  total  hardness  20.  Much.  MgClj  is  present,  and 
the  water  is  unfit  for  domestic  use. 

Sample  No.  7  contains  much  acid,  and  could  not  be  allowed  to 
traverse  lead  pipes.  Its  organic  XH3  and  0  absorbed  are  not  so 
high  as  in  many  peaty  waters. 


WATERS  FROM  VARIOUS  SOURCES 


y;< 


Physical  characters     -         -  - 

Reaction    -         -         -          .  . 
Free  and  saline  NH3  -         -  - 
Organic  NHo       -         -          -  _ 
CI       -         -"        - 
Nitrous  N            -         -         _  . 
Nitric  N     -         -         -         -  - 
Hardness  (total)          _         .  _ 
,,         (permanent) 
(temporary) 
O  absorbed  at  37°  C.  in  three  hours 
Metals  (Zn,  Pb,  Fe,  Cu) 
Solids  (total)       -         -         -  . 
(volatile)           -         -  - 
,,      (fixed)      -         -         -  - 
Appearance  on  ignition 
Microscopic  examination  of  sedi- 
ment      -         -         -         -  - 
Bacteriological  examination 


No.  7. 
Surface  Water,  Peaty. 

No.  3. 
Surface  Water,  not  Peaty. 

Colour     brownish; 

slight  taste 

Acid 

Almost  colourless, 
no  taste 
Neutral 

O'OOI 

0-002 

0-030 

0-003 

0-600 
NU 

0-800 

Nil 

O-OIO 

3-000 

0-030 
3-000 

3-000 

Nil 

2-500 
0-500 

0-150 

Nil 

0-050 

Nil 

9-000 

4-000 

2-000 

I -000 

7-000 
Charring 

3-000 
Faint  darkening 

Vegetable  debris 
No   intestinal   or- 

Nil 
No   intestinal   or- 

ganisms 

ganisms 

Samples  Nos.  9  and  10  were  taken  from  the  same  house.  The 
analysis  of  10,  carried  out  a  month  after  that  of  9,  shows  some  slight 
variations,  which  are  to  be  expected,  when  it  is  remembered  that 
the  composition  of  river  water  varies,  with  its  varying  powers  of 


Physical  characters     -         -  - 

Reaction     -         -         -         -  . 

Free  and  saline  NH3  -         -  - 

Organic  NHo       -         -         -  . 

CI       -----  - 

Nitrous  N  - 

Nitric  N      -         -          -         -  - 

Hardness  (total)          -         -  - 

,,  (permanent) 

,,          (temporary) 
O  absorbed  at  37°  C.  in  three  hours 
Metals  (Zn,  Fe,  Pb,  Cu) 
Solids  (total)       -         -         -  _ 
(volatile)  -         -         -  . 
,,      (fixed)       -         -         -  . 
Appearance  on  ignition 
Microscopic  examination  of  sedi- 
ment       -         -         -         -  . 
Bacteriological  examination 


No.  9. 

New  River  Water  from 

the  Lea. 

No.  10. 

New  River  Water  from 

the  Lea. 

Excellent 

Slightly  alkaline 

Nil 

Excellent 
SUghtly  alkaline 

O-OOI 

0-002 
1-900 

Nil 
o-i6o 

0-003 

I -8600 

Nil 

0-2I0 

20-500 

21-500 

11-500 
9-000 

13-500 
8-000 

0-017 

Nil 

32-600 

I0-200 

0-023 

Nil 
28-560 
10-000 

22-400 

Nil 

18-560 

Nil 

Nil 


Nil 


94 


PRACTICAL  SAXITARY  SCIENCE 


self-purification,  with  the  nature  of  the  strata  in  which  its  springs 
of  origin  occur,  and  of  the  strata  over  which  it  flows,  and  with  the 


No.  11. 

No.  12. 

Peaty  Water. 

Well  Water. 

Physical  characters     - 

. 

Colour  light-brown 

Excellent 

Reaction    -         -         - 

- 

Acid 

Neutral 

Free  and  saline  NH3  - 

- 

0-005 

Nil 

Organic  NHo 

- 

0-026 

o-ooi 

CI       -         -         - 

- 

1-500 

3-800 

Nitrous  N  - 

- 

Nil 

Nil 

Nitric  N     -         -         - 

- 

0-220 

0-362 

Hardness  (total) 

- 

3-500 

26-000 

(permanent) 

- 

3-500 

12-300 

(temporary) 

- 

Nil 

14-000 

0  absorbed  at  37°  C.  m  three  hours 

0-146 

0-008 

Metals  (Zn,  Fe,  Pb,  Cu) 

- 

Nil 

Nil 

Solids  (total) 

- 

12-300 

38-260 

,,     ^ volatile)  - 

- 

S-300 

8-500 

„      (fixed) 

- 

4-000 

29-760 

Appearance  on  ignition 

- 

Charring 

Nil 

Microscopic  examination  of  sedi- 

ment      -         .         - 

- 

Vegetable  d6bris 

Nil 

Bacteriological  examination 

Negative 

Nil 

nature  of  the  soils  and  subsoils  of  its  basin,  especially  in  regard  to 
cultivation,  density  of  population,  and  the  presence  of  sewage  and 
industrial  waste. 


Physical  characters     -         -         - 
Reaction    ----- 

Free  and  saline  NH3  -         -         - 
Organic  NH3       -         -         _         - 
CI       -----         - 

Nitrous  N  - 

Nitric  N      -  -  -  -  - 

Hardness  (total)  -         -         - 

(permanent) 
(temporary) 
O  absorbed  at  37°  C.  in  three  hours 
Metals  (Zn,  Fe,  Pb,  Cu) 
Solids  (total)       -         -         -         - 

,,     (volatile)  -         -         -         - 

.,     (fixed)       -         -  -         - 

Appearance  on  ignition 
Microscopic  examination  of  sedi- 
ment      ----- 

Bacteriological  examination 


No.  13. 
Lambeth  Supply. 

No.  14. 
Chelsea  Supply. 

Excellent 

Excellent 

Faint  alkaline 

Neutral 

Nil 

Nil 

0-005 

0'002 

1-850 

Nil 

I -740 

Nil 

0-086 

0-009 

18-600 

18-400 

S-500 

8-400 

lO-IOO 

10-000 

0-043 
Nil 

0-023 

Nil 

26-400 
6-800 

26-720 
6-400 

ig-600 

20-320 

Nil 

Nil 

Nil 

Nil 

Nil 

Nil 

WATERS  FROM  VARIOUS  SOURCES 


05 


Sample  No.  ii  is  plumbo-solvent,  and  is  slightly  polluted  with 
animal  matter,  in  that  free  and  saline  NHg,  CI,  and  nitric  N,  arc  too 
high  for  a  peaty  water. 

Sample  No.  12  is  a  pure  water  from  a  deep  well  in  Kent. 

Samples  Nos.  13  and  14  are  fair  specimens  of  filtered  Thames 
water. 

In  the  '  nil '  returns  of  the  bacteriological  and  sediment  examina- 
tions, it  is  to  be  understood  that  nothing  was  found  indicative  of 
animal  pollution. 


A  'Dorset  Water-Supply. 

Three  samples  selected  from  a  series  of  thirteen  investigated  at 
the  same  time  by  the  writer,  and  showing  the  changes  effected  by 
treatment  with  chalk  and  filtration.  These  waters,  derived  from 
Bagshot  sands,  covered  with  peat,  are  acid  and  ferruginous. 


(A) 

(B) 

(C) 

Before  Treatment 

After  Treatment 

A  fhpr  P'iltrr)  tinn 

with  Chalk. 

with  Chalk. 

^A.ILr:r    r  llli  dLlUil. 

Physical  characters — 

Colour,  smell,  turbidity 

Good 

Good 

Excellent 

Chemical  reaction 

Acid 

Acid 

Acid 

Acidity  =  ) 

0-500 

0-350 

2-190  HClj 

Free  and  saline  NH3 

O'OiS 

0-022 

O-OOI 

Organic  NH3    -         -         -          - 

o-oi6 

o-oio 

O-OOI 

0  absorbed  in  three  hours  at 

37°  C.            .         -         -         - 

0-040 

0-020 

Nil 

Total  solids      -         -         -         - 

12-300 

11-500 

11-500 

Hardness  (total)       -         -         - 

2-500 

2-500 

2-700 

(temporary) 

— 



— 

(permanent) 

2-500 

2-500 

2-700 

Chlorine  ----- 

2-500 

2-000 

2-500 

Nitric  N  - 

O-IOO 

O-IOO 

O-OIO 

Iron  in  solution        _         _         . 

0-325 

0-220 

O-IIO 

As  the  filtered  water  still  contains  acidity,  it  may  not  be  passed 
through  lead  pipes. 

Sea  water  contains  in  100,000  parts  nearly  2,000  parts  CI,  and 
between  3,000  and  4,000  parts  total  solids.  Hardness  ranges 
between  500  and  600  parts.  Lime  and  magnesia  together  form 
about  240  parts,  and  the  ratio  of  the  first  to  the  second  is  about 
I  :6. 


96 


PRACTICAL  SANITARY  SCIENCE 


The  following  is  an  estimation : 

In  icx5,ooo  pts 

Free  and  saline  XH3            -         .         .         .         .  o-oo6 

,    Total  solids        -------  3,380-000 

Lime          --------  35-000 

Magnesia   --------  205-000 

Silicia         --------  0-450 

Hardness    --------  580-000 

Chlorine     --------  1,875-000 

The  table  below  represents  the  comparative  figures  for  the 
principal  chemical  constituents  of  a  well-filtered  river  water, 
delivered  to  a  town  of  some  40,000  inhabitants,  and  the  sewage  of 
the  same  town  before  treatment : 


Water. 

Sewage. 

Free  and  saline  NH3     -         -         - 

Nil 

6-800 

Organic  NH3         -         -         -         - 

0-002 

2-000 

0  absorbed  in  two  hours  at  So°  F. 

0-020 

4-080 

Chlorine       ----- 

1-850 

1 1 -800 

Nitric  X       -         -         -         -         - 

0-120 

Nil 

Total  solids-         -         -         -         - 

28-500 

160-000 

CHAPTER  VIII 

SEWAGE  EFFLUENTS 

An  average  sample  of  the  day's  working  should  in  all  cases  be 
obtained,  and  the  analysis  performed  forthwith. 

It  has  been  usual  to  estimate  the  '  free  and  saline  '  and  '  albu- 
minoid '  NHg,  0  absorbed  from  permanganate,  total  solids,  solids 
in  solution,  suspended  matter,  oxidized  N,  and  CI. 

The  physical  characters  may  be  noted,  and  incubation  at  37°  C. 
for  forty-eight  hours  may  be  effected  in  order  to  determine  the 
presence  or  absence  of  further  fermentation,  as  indicated  by  odour. 

The  analysis  is  frequently  required  for  the  determination  of  the 
degree  of  purification  at  a  particular  stage,  or  the  comparative  value 
of  a  certain  method  of  sewage  treatment.  It  is  usual  to  record  the 
purification  as  percentages  of  the  figure  for  albuminoid  NHg.  If, 
for  example,  before  treatment  the  albuminoid  figure  is  0  -6  part  per 
100,000,  and  after  treatment  0-15,  it  is  clear  that  purification  has 
taken  place  to  the  amount  of  0-45  part  per  100,000,  or  75  per  cent, 
of  the  original  albuminoid  NH3  has  been  oxidized. 

The  ammonias  are  estimated  as  described  under  water,  but  a  large 
dilution  of  the  effluent  is  necessary;  10  c.c.  may  be  made  up  to 
1,000  c.c.  with  distilled  water,  and  in  some  instances  5  c.c.  in  the 
same  volume  will  be  convenient. 

The  0  absorbed  from  permanganate  is  estimated  by  Tidy's 
process,  and  care  should  be  taken  that  sufficient  permanganate  is 
added  from  time  to  time,  and  that  the  flask  is  frequently  shaken. 
A  convenient  dilution  is  10  c.c.  in  a  litre. 

In  the  working  out  of  this  process  it  should  be  noted  that  various 
bodies  besides  organic  matter  absorb  0  from  permanganate,  such 
as  nitrites,  sulphites,  sulphides,  sulpho-cyanates,  numerous  d3^es, 
and  vaiious  coal-tar  products. 

97  7 


98  PRACTICAL  SAXITARY  SCIENCE 

Total  solids  are  estimated  by  evaporating  lOO  c.c.  of  the  sample 
in  a  platinum  dish  on  a  water-bath.  When  dry,  the  dish  is  trans- 
ferred to  an  air-bath,  and  dehydration  continued.  It  is  then  passed 
through  a  desiccator,  and  weighed.  The  difference  between  this 
weight  and  that  of  the  dish  represents  the  '  total  solids.' 

The  solids  in  suspension  are  found  by  passing  loo  c.c.  of  the 
sample  through  two  folds  of  lilter-paper,  whereby  the  solids  in 
solution  alone  pass  through.  The  filtrate  is  evaporated  to  dryness, 
further  delu'drated,  desiccated,  and  weighed.  The  result  represents 
the  '  solids  in  solution.'  The  difference  between  this  weight  and 
that  of  the  total  solids  represents  the  '  solids  in  suspension.' 

In  estimating  nitrous  N,  dilute  the  liquid  with  distilled  water 
(free  from  nitrite)  to  a  convenient  strength.  Take  lOO  c.c.  in  a 
Xessler  glass,  as  described  under  water,  add  i  c.c.  metaphenylene- 
diamine  and  i  c.c.  HoSOj  (i  in  j).  Match  by  treating  in  a  similar 
manner  a  standard  solution  of  potassium  nitrite  made  up  to  lOO  c.c. 
Stand  for  twenty  minutes  before  comparing. 

The  nitric  N  is  estimated  by  Crum's  method  or  by  the  copper- 
zinc  couple.  A  convenient  dilution  must  be  made.  Where  time  is 
an  item,  as  in  examinations,  the  less  accurate  phenol  sulphonic  acid 
method  may  be  used. 

If  raw  sewage  is  to  be  anal3'zed,  weaker  dilutions  must  be  used — 
5  c.c.  or  less  in  a  litre. 

In  the  distillations  carried  out  in  Wanklyn's  process  the  volume 
of  the  boiling  fluid  should  never  be  allowed  to  fall  below  150  c.c. 
Hot,  ammonia-free  distilled  water  when  necessary  should  be  added. 

Griess's  test  should  be  promptly  performed,  and  if  the  fluid  is  not 
transparent  it  should  be  filtered  before  adding  the  reagents. 

Estimation  of  the  total  X  by  Kjeldahl's  method  is  a  much  more 
accurate  index  of  the  organic  pollution  than  that  by  Wanklyn's 
process  for  albuminoid  ammonia.  The  latter  usually  gives  less 
than  half  the  N  figure  obtained  by  the  former. 

With  a  little  practice  Kjeldahl's  method  can  be  carried  out  rapidly 
and  accurately  as  follows: 

In  a  Kjeldahl  flask  put  10  c.c.  sewage  effluent  and  i  c.c.  H2SO4, 
and  evaporate  on  a  water-bath  to  half  the  biilk.  When  cool,  add 
about  10  c.c.  oil  of  vitriol,  and  about  10  grammes  sulphate  or  bisul- 
phate  of  potassium  (to  raise  the  boiling-point).  Digest  under  a 
hood  in  a  draught-chamber.     Continue  the  digestion  until  the  solu- 


SEWAGE  EFFLUENTS  'yj 

tion  is  a  pale,  transparent  yellow  colour — i.e.,  initil  ;ill  the  C  lias 
been  completely  oxicliz;ed.  Cool  and  wash  out  into  ;i.  distilling- 
flask.  Make  up  to  500  c.c.  with  ammonia-free  distilled  water;  add 
excess  KOH  and  a  piece  of  ignited  pumice-stone,  and  distil  over 
nearly  350  c.c.  Nesslerise  the  ammonia  collected,  and  subtract 
from  the  result  the  amount  of  free  and  saline  ammonia  previously 
estimated.  The  difference  is  the  NHg  due  to  organic  nitrogen. 
The  reagents  used  should  be  free  from  NHg. 

Digestion  with  concentrated  H2SO4  converts  the  N  into  (XH4)oS04. 
Subsequent  addition  of  excess  of  KOH  decomposes  (NH4)oS04, 
with  liberation  of  NHg,  which  is  distilled  over. 

Instead  of  Nesslerising,  the  NHg  can  be  received  in  excess  of 
standard  acid,  and  the  unsaturated  acid  finally  titrated  with  alkali : 
the  amount  of  acid  saturated  is  equivalent  to  the  XHg  from  which 
the  N  is  at  once  calculated. 

The  purification  of  sewage  has  little  influence  on  the  amount  of  its 
chlorine,  which  in  average  samples  reaches  10  or  11  parts  per  100,000. 

A  sewage  effluent  should  be  colourless  and  without  odour. 

The  albuminoid  NHg  should  not  exceed  o-i  to  0-15  part  per 
100,000,  nor  the  0  absorbed  in  four  hours  at  2y°  C  i  to  1-5  parts. 
CI  and  free  and  saline  NHg  are  unimportant. 

The  pouring  of  crude  sewage  or  badly  purified  effluents  into  rivers 
of  limited  volume  will  cause  deoxidation  of  the  water,  with  con- 
sequent injury  to  fish  and  other  forms  of  aquatic  life,  putrefac- 
tion of  organic  matter  with  resulting  nuisance,  growth  of  sewage 
fungus,  disposition  of  suspended  matters,  etc. 

In  order  to  determine  the  condition  of  contaminated  streams  in 
respect,  of  odour,  development  of  grey  algse,  accumulation  of  putre- 
fying sewage  solids,  and  injury  to  fish  life,  the  Sewage  Commissioners 
{1898,  still  sitting)  have  confined  their  attention  mainly  to  three  tests : 

1.  The  amount  of  ammoniacal  N. 

2.  The  amount  of  0  absorbed  from  permanganate  in  four  hours. 

3.  The  amount  of  dissolved  0  taken  up  in  five  days. 

Whilst  the  ammoniacal  N  may  be  considered  as  the  most  delicate 
chemical  index  of  recent  sewage  pollution,  it  is  not  equally  reliable 
in  demonstrating  the  character  of  the  pollution  as  indicated  by 
the  effect  which  the  sewage  produces  on  the  stream.  The  nuisance- 
producing  power  of  a  sewage  or  effluent  is  broadly  proportional  to  its 
power  of  deoxygenating  the  water  of  the  stream,  and  tests  based  on 


100  PRACTICAL  SAXITARY  SCIENCE 

tlie  rate  and  degree  of  absorption  of  O  are  the  most  trustworthy  for 
determining  whether  or  not  nuisance  is  likely  to  occur  in  a  stream. 
The  five  days'  test  represents  naturally  the  actual  process  by  which 
the  more  readily  oxidizable  constituents  of  the  polluting  matter 
absorb  the  0  dissolved  in  the  ri\-er-water,  and  shows  smaller  differ- 
ences in  quality  of  water. 

The  pennanganate  process  may  give,  approximately,  the  same 
figure  for  a  water  polluted  with  tank  liquor  and  for  a  water  polluted 
with  filter  eftluent,  while  the  five  days'  dissolved  0  test  will  give  a 
liigher  figure  for  the  water  polluted  with  tank  liquor,  thus  indicating 
differences  in  kind  as  well  as  in  degree  of  pollution. 

The  Commissioners  conclude  that  if  loo.ooo  c.c.  of  river  water  do 
not  take  up  more  than  0-4  gramme  dissolved  0  in  five  days,  the 
river  will  be  free  from  signs  of  pollution;  but  that  if  it  takes  up  a 
higher  figure  it  will  most  probably  show  signs  of  pollution.  This 
number  0-4  they  term  the  limiting  figure,  and  regard  it  as  the  best 
foundation  on  which  to  construct  a  scheme  of  standards. 

As  results  will  be  found  to  vary  according  to  temperature,  they 
adopt  the  temperature  of  65^  F.  (18-3°  C),  and  in  order  to  provide 
a  wide  margin  of  safety  the  dr}-  weather  flow  of  the  ri\-er. 

It  will  be  seen  that  the  amount  of  dissolved  O  taken  up  in  five 
da\^s  by  a  mixture  of  river  water  and  sewage  depends — (i)  on  the 
am.ount  taken  up  by  the  sewage  liquor;  (2)  on  the  amount  taken 
up  by  the  river  water ;  (3)  on  the  proportion  in  which  the  two  liquids 
are  mixed. 

If  a;  =  parts  of  dissolved  0  taken  up  per  100,000  by  sewage; 
y=parts  of  dissolved  0  taken  up  per  100,000  by  river  water 

above  outfall ; 
z  =  dilution  (proportion  of  ri\-er  water  to  sewage) ; 

then  — ^  =  0-4. 

Thus,  if  an  effluent  which  takes  up  o'l  part  dissolved  0  in  five 
days  be  discharged  into  ten  times  its  volume  of  water,  we  get — 

;»;-l-(o-i  X  10) 

10  + 1  ^ 

x  +  i  =4-4 
A'' -3-4 


SEWAGE  EEFIJJENTS  loi 

— that  is,  in  this  case,  the  effluent  may  be  allowed  to  take  up  3-4 
parts  dissolved  0  per  100,000  in  five  days,  which  figure  would  be 
the  standard  for  this  particular  discharge. 

The  most  important  local  condition  is  the  degree  of  dilution 
afforded  by  a  river  to  the  contaminating  discharge.  It  is  advised 
that  a  standard  effluent  should  not  contain  more  than  3  parts 
suspended  solids  per  100,000,  and  that  samples  which  satisfy  this 
test  must  also  be  considered  in  relation  to  the  five  days'  test.  The 
latter  is  fixed  at  2  parts  per  100,000. 

An  effluent  which  takes  up  2  parts  per  100,000  dissolved  0  in 
five  days  will  need  some  dilution  if  nuisance  is  to  be  avoided.  The 
minimum  degree  of  dilution  required  for  safety  can  be  found  from 
the  formula: 

2  +  (o-2  xz) 
^^ =0-4, 


It. is  considered  safe  to  assume  that  the  majority  of  effluents  are 
diluted  by  more  than  eight  times  their  volume  of  river  water. 

It  is  recommended,  therefore,  that  an  effluent  should  not  contain 
more  than  3  parts  suspended  matter  per  100,000,  and  that,  including 
its  suspended  matter,  it  should  not  take  up  more  than  2  parts  dis- 
solved 0  per  100,000  in  five  days  at  18-3°  C.  It  is  suggested  that 
this  be  considered  the  normal  standard  for  effluents.  An  effluent 
is  considered  satisfactory  that  contains  less  than  3  parts  per  100,000 
suspended  solids,  and  which,  after  filtration,  does  not  absorb  in  parts 
per  100,000  more  than  0-5  dissolved  0  in  twenty- four  hours,  or 
1*0  part  in  forty-eight  hours,  or  1-5  parts  in  five  days. 

Adeney's  method  of  determining  the  rate  of  absorption  of  dis- 
solved O  by  polluted  waters  is  described  in  detail  in  the  Fifth  Report 
of  the  Royal  Commission  on  Sewage  Disposal. 

The  Report  (Cd.  4,278,  1908)  states  that  effluents  which  are  de- 
rived from  strong  original  liquids  may  often  contain  large  amounts 
of  organic  matter  in  solution,  and  yet  not  take  up  dissolved  oxygen 
rapidly  from  water  or  cause  injury  to  the  streams  into  which  they 
are  discharged.  Such  effluents,  judged  by  the  empirical  tests 
hitherto  in  common  use,  might  be  regarded  as  polluting  liquids. 
The  effect  of  an  effluent  on  a  stream  does  not  depend  on  the  absolute 
amount  of  organic  matter  in  it,  but  on  the  nature  and  condition  of 


102  PRACTICAL  SAXITARY  SCIENCE 

that  organic  matter,  and  the  important  thing  to  ascertain  is  the 
extent  to  wliich  the  original  organic  matter  has  undergone  fermenta- 
tion. Dunbar  has  sliown  that  after  a  certain  percentage  purification 
tlie  residual  organic  matter  in  certain  sewages  is  so  altered  as  to 
be  non-putrescible. 

To  determine  the  rate  of  absorption  of  dissolved  0,  it  is  only 
necessary  to  ascertain  by  a  volumetric  process  the  amount  of  dis- 
solved O  in  the  effluent  when  fresh,  and  in  a  portion  of  the  same 
effluent  after  it  has  been  kept  for  a  definite  period  of  time — two  to 
live  days.  The  difference  between  the  two  estimations  will  give 
the  amount  of  0  absorbed  during  the  time  of  keeping,  and  the  rate 
of  absorption  may  be  taken  to  be  uniform,  at  least  for  the  first  two 
days  of  obser\-ation. 

If  a  knowledge  of  the  attendant  changes  wliich  take  place  during 
the  various  stages  of  the  fermentation  be  required,  it  will  be  neces- 
sary, in  addition  to  estimation  of  the  dissolved  O,  to  determine  the 
NH.J  and  HNOo  and  HNO.j  before,  during,  and  after  period  of 
fermentation. 

For  most  practical  purposes  it  is  only  necessary  to  determine 
the  rate  and  total  absorption  of  ox\'gen  and  the  character  of  the 
fermentation,  whether  a  carbon  or  nitrogen  one.  The  first  can  be 
done  by  estimating  the  loss  of  0  in  the  atmosphere  of  the  flask  con- 
taining the  polluted  water,  and  the  second  by  ascertaining  whether 
nitrites  and  nitrates  have  been  formed  or  not.  In  most  cases,  how- 
ever, as  Adeney  shows,  even  this  will  be  found  unnecessary,  as  the 
completion  of  the  carbon-oxidation  stage  of  fermentation  will  be 
indicated  by  the  cessation  of  the  absorption  of  oxygen  which  occurs 
during  the  interval  of  rest  which  takes  place  before  the  commence- 
ment of  the  nitrogen-oxidation  stage. 

The  Process. — A  measured  quantitv  of  the  polluted. water  (loo- 
250  c.c,  according  to  amount  of  polluting  matters  contained)  is 
decanted  into  B,  into  which  a  little  freshly  precipitated  magnesium 
hydrate  has  been  previously  placed  for  the  purpose  of  fixing  the 
("Oo  in  the  water.  A  similar  volume  of  distilled  watei  is  poured  into 
A.  Similar  volumes  of  air  are  thus  left  in  the  two  bottles.  These 
volumes  should  be  sufficiently  large  (capacity,  a  litre  or  more)  to 
c  nsure  much  more  0  in  B  than  can  possibly  be  used. 

Corks,  connecting-tube,  and  stopcocks  are  fitted.     A  slight  rise  of 


SE  VVA  GE  EFFL  (JEN  J.  S 


103 


capillary  water  will  occur  in  the  portion  of  the  connecting-tube  in  A. 
The  height  of  this  capillary  column  is  marked  with  a  diamond  or 
file;  the  mark  serves  as  an. index  for  subsequent  measurement. 
With  both  stopcocks  open  the  two  bottles  are  immersed  in  a  water- 
bath  for  a  few  minutes  to  allow  of  their  contents  assuming  a  common 
temperature.  Both  stopcocks  are  then  closed,  and  the  temperature 
of  the  bath  and  the  height  of  the  barometer  are  noted. 

The  bottles  are  taken  out  of  the  water-bath  and  dried.     When 
completely  dry  the  corks  are  coated  with  shellac  varnish  to  prevent 


Fig.  23 

diffusion  of  air  through  them.  The  apparatus  is  then  put  in  a 
mechanical  shaker,  which  keeps  the  contents  in  gentle  motion. 

As  0  is  absorbed  by  the  polluted  water  in  B,  the  pressure  of  the 
atmosphere  is  reduced  relatively  to  that  of  the  atmosphere  in  A, 
which  is  unaffected  by  the  distilled  water.  Accordingly,  water  from 
A  will  rise  in  the  connecting-tube  in  proportion  to  the  volume  of  O 
absorbed  by  the  polluted  water  from  the  atmosphere  in  B. 

This  volume  of  0  can  be  measured  at  anj''  time  by  attaching  by 
means  of  a  flexible  tube  a  burette  containing  distilled  water  at  the 
temperature  of  the  laboratory.     As  the  water  from  the  burette  is 


104  PRACTICAL  SAXITARY  SCIENCE 

cautiously  allowed  to  flow  into  B  the  water  in  the  comiecting-tube 
will  gradually  sink  back  to  the  index,  at  which  instant  the  stopcock 
to  B  is  closed.  The  reading  on  the  burette  is  equal  to  the  volume  of 
O,  which  has  been  absorbed  from  the  atmosphere  of  B  at  the  tem- 
perature and  pressure  obtaining  at  the  commencement  of  the  ex- 
periment. 

The  distilled  water  bottle  A  acts  as  a  reference  pressure  bottle. 
If  a  comparatively  rapid  absorption  of  0  occurs  during  the  first  hour 
or  two  and  this  is  followed  by  a  slower  and  regular  absorption,  it 
may  safely  be  taken  to  be  due  to  the  polluted  water  being  de-aerated 
to  start  with,  and  possibly  also  to  the  presence  of  easily  and  directly 
oxidizable  substances  in  it;  the  subsequent  slower  and  regular 
absorption  being  due  to  indirect  oxidation  accompanying  the  fer- 
mentation of  the  polluting  matters. 

It  is  very  important,  as  noted  above,  that  sufficient  excess  of  air 
be  always  secured,  other^vise  the  operation  is  open  to  certain  obvious 
inaccuracies.  The  replacement  of  the  absorbed  0  by  water  is 
equivalent  to  increasing  the  pressure  of  the  N  in  B,  which  will  lead 
to  absorption  of  N  by  the  polluted  water  and  the  distilled  water 
added  to  it,  unless  the  air  in  the  bottle  be  in  such  large  excess  that 
the  0  absorbed  be  only  a  small  fraction  of  it.  Further,  with  in- 
sufficient air  there  may  be  such  a  reduction  in  the  store  of  0  in  the 
atmosphere  of  B  as  to  lead  to  appreciable  reduction  in  the  rate  of 
fermentation  in  the  polluted  water. 

Bacteriological  Examination  of  Sewage  and  Sewage  Effluents. — 
Houston's  method  of  water  examination  is  equally  suitable  for 
sewage  effluents  and  sewage  when  these  have  been  properly  diluted. 
In  the  estimation  of  B.  coli  it  may  be  necessary  to  work  on  as  small 
a  quantity  as  o -000001  or  even  o-oooooooi  c.c.  of  sewage. 


CHAPTER  IX 
SOIL 

Analysis  of  Soils. 

The  analysis  of  soils  is  a  large  subject,  and  requires  for  its  proper 
execution  a  special  training  in  chemistry.  For  public  health  pur- 
poses, however,  very  few  estimations  are  required,  and  these  are 
of  a  simple  kind.  The  powers  which  a  soil  possesses  for  absorbing 
and  retaining  moisture  are  of  some  importance,  but  direct  examina- 
tion of  the  soil  and  subsoil  in  position  in  a  given  locality  will 
furnish  more  valuable  information  than  laboratory  tests. 

The  capacity  for  absorbing  moisture  may  be  estimated  by  means 
of  a  percolator  and  burette.  A  quantity  of  dried  soil  (say  lOO 
grammes)  is  flooded  with  water  for  two  hours  and  allowed  to  drain  for 
four  hours.  The  difference  in  the  reading  of  the  burette  before  and 
after  the  operation  gives  the  number  of  c.c.  of  water  absorbed  by 
100  grammes,  or  the  absorption  per  cent. 

Perhaps  a  simpler  method  is  the  following : 

One  hundred  grammes  of  dried  soil  are  covered  with  water  in  a 
cylinder.  Sufficient  time  is  allowed  for  saturation,  which  in  the 
case  of  clay  soils  may  be  several  hours.  The  water  is  drained  off 
through  a  muslin  filter,  and  the  soil  is  reweighed.  The  increase  in 
weight  roughly  represents  the  percentage  absorption. 

The  determination  of  the  size  of  the  particles  of  a  soil  is  carried 
out  by  using  a  series  of  sieves  possessing  meshes  of  2  millimetres, 
I  millimetre,  and  0  -5  millimetre  respectively.  A  number  of  meshes 
larger  than  2  millimetres  may  be  used. 

One  hundred  grammes  of  dried  soil  are  pulverized  with  the  fingers. 
The  larger  pebbles,  roots,  etc.,  are  removed  and  weighed.  The  residue 
is  transferred  to  the  2 -millimetre  sieve,  and  when  all  has  passed 
that  will,  the  remainder  is  further  rubbed  between  the  fingers,  and 

105 


io6  PRACTICAL  SAXITARV  SCIEXCE 

once  moic  shaken  on  tlie  sieve.  What  remains  on  this  sieve  is 
weighed.  In  like  manner  the  amounts  left  on  the  other  sieves  are 
weighed.  Finally,  tlie  soil  wliich  passes  the  5-millimetre  sieve 
is  weighed,  and  the  results  are  collected  as  (a)  coarse  masses  removed 
by  hand,  (/;)  masses  kept  back  by  the  2-millimetre  sieve,  (c)  sand 
retained  by  the  i -millimetre  sieve,  {d)  fine  sand  retained  bj^  the 
o-5-milIimetre  sieve,  and  (e)  fine  soil  passing  the  0-5 -millimetre  sieve. 

The  specific  heat  of  soils  is  determined  by  a  sensitive  calorimeter. 
The  specific  heat  ranges  from  0-2  to  o-3.  and  is  greatest  in  peaty 
soils. 

The  determination  of  the  porosity  of  a  soil  is  effected  by  linding 
the  real  and  apparent  specific  gravity  of  the  soil,  and  di\'iding  the 
latter  by  the  former. 

The  real  specific  gravity  is  obtained  by  ])lacing  in  a  50  c.c.  specific 
gravity  bottle  10  grammes  of  the  soil  dried  at  100°  C.  to  constant 
weight,  rinsing  the  last  particles  into  the  bottle  with  distilled  water, 
and  making  up  with  distilled  water  to  the  mark.  The  whole  is 
weighed  at  15°  C  The  weight  of  the  water  displaced  by  the  10 
grammes  of  soil  is  thus  easil}'  calculated.  The  weight  of  the  soil — 
viz.,  10  grammes — divided  by  the  weight  of  displaced  water  is  the 
specific  gravity. 

The  apparent  specific  gravity  is  obtained  by  filling  a  1,000  c.c. 
cylinder  with  soil,  introduced  in  small  quantities  at  a  time,  and 
thoroughly  settled  in  tlie  cylindei  b}-  tapping  from  time  to  time 
on  the  bench.  When  full  the  cylinder  is  covered  with  a  glass  plate 
and  weighed.  The  weight  of  the  soil  (cylinder  full  -  cylinder  empty) 
divided  by  1,000  is  the  apparent  specific  gravity. 

The  real  specific  gravity  of  a  sample  was  found  to  be  2*46,  and 

the-  apparent  1*36;  the  porosity  is  therefore  :^f  =  0-55,  or  expressed 

as  a  percentage  =  55  per  cent. 

Pore  volume,  or  porosity,  being  the  sum  total  of  the  interstitial 
spaces  which  may  be  filled  with  water  or  air,  or  both,  does  not  depend 
on  the  size  of  the  particles  but  on  their  uniformity,  or  want  of 
uniformity,  of  size,  and  on  their  arrangement.  The  porosity  of  a 
soil  composed  of  unifonn  spherical  particles  the  size  of  peas  is  the 
same  as  that  of  another  composed  of  particles  the  size  of  small 
shot,  and  in  each  case  is  about  one-third  of  the  whole. 


SOIL  107 

Permeability  of  soil  to  air  depends  not  on  the  amcjunt  of  its  pore 
volume,  but  on  the  size  of  the  individual  spaces.  Permeability 
diminishes  to  an  extraordinary  degree  with  diminution  of  the  size 
of  the  particles. 

The  water  retained  in  soil  exists  as  hygroscopic  water  adherent 
by  surface  attraction  to  the  soil  grains,  and  as  capillary  water  held 
up  in  the  capillary  spaces.  The  latter  constitutes  by  far  the  larger 
portion  of  the  retained  moisture.  If  the  texture  of  a  soil  be  so  fine 
that  all  spaces  are  within  the  limits  of  capillary  magnitude,  the 
maximum  water-retaining  power  is  attained. 

The  differentiation  of  the  constituents  of  soils  into  sand,  clay, 
and  organic  matter  is  of  some  importance. 

Sand  consists  of  the  coarser  particles  which  rapidly  sink  in  water ; 
clay  of  the  fine  particles  which  remain  for  a  time  in  suspension. 

The  estimation  of  sand  and  clay  may  be  performed  thus:  Take 
10  grammes  of  dried  soil  in  a  beaker.  Moisten  the  soil  with  a  little 
distilled  water  and  a  few  drops  of  a  solution  of  NH^Cl.  When 
moist  add  80  to  100  c.c.  distilled  water,  and  stir.  Allow  to  settle 
for  five  minutes,  and  pour  off  the  fluid  into  a  tall  cylinder.  Another 
100  c.c.  of  water  is  added,  and  the  soil  well  stirred.  After  settling 
again  for  five  minutes  the  fluid  is  poured  off  into  the  cylinder. 
These  manipulations  are  repeated  until  the  overlying  fluid  is  quite 
clear. 

The  sand  is  turned  on  to  a  filter-paper,  well  washed,  dried,  weighed, 
and  recorded  as  sand. 

The  cylinder  is  set  aside  for  twenty-four  hours,  and  when  fully 
settled  the  upper  portion  of  the  fluid  is  run  through  a  filter-paper 
without  disturbing  the  sediment.  When  nearly  all  the  water  has 
been  drained  off,  the  sediment  is  stirred  and  poured  on  the  filter. 
The  last  traces  of  clay  are  washed  from  the  cylinder,  and  the  entire 
contents  now  on  the  filter  are  thoroughly  washed,  dried,  weighed, 
and  recorded  as  clay. 

Clay  soil  contains  over  30  percent,  clay;  some  brick  clays  contain 
95  per  cent.  Sandy  soils  contain  as  little  as  i  or  2  per  cent,  clay; 
a  loam  contains  10  per  cent. 

In  order  to  determine  the  amount  of  organic  matter  in  a  soil,  take 
10  grammes  of  a  dried  sample  in  a  platinum  dish,  and  heat  it  at  a 
temperature  a  little  over  100°  C.  until  a  constant  weight  is  obtained. 


io8  PRACTICAL  SAX  IT  A  RY  SCIENCE 

Oxidize  over  a  flame  at  a  low  red  heat,  transfer  to  desiccator,  and 
weigh.  The  loss  in  weiglit  gives  roughly  the  amount  of  organic 
matter. 

Lime  mav  be  estimated  thus:  Dissolve  a  few  grammes  of  the  dried 
soil  in  dilute  HCl,  and  dilute  the  resulting  solution  to  about  lOO  c.c. 
with  water.  Heat,  add  NH4OH  in  slight  excess,  and  a  solution  of 
ammonium  oxalate  also  in  slight  excess.  Allow  the  precipitate 
to  settle  in  a  wami  place.  Pass  the  clear  liquid  through  a  small 
filter  and  then  bring  the  precipitate  upon  it.  Wash  with  hot 
water  and  set  the  filtrate  and  washings  aside.  Push  the  precipi- 
tate and  filter-paper  through  the  funnel  into  a  flask,  add 
some  H2SO4,  dilute  freely,  warm  to  60°  or  70°,  and  run  in  ^^  per- 
manganate until  faint  pink  remains.  Each  c.c.  of  f"^  permanganate 
represents  0*0028  gramme  CaO. 

Magnesia. — Evaporate  the  filtrate  and  washings  to  small  bulk  on 
the  water-bath,  render  alkaline  with  XH4OH,  add  sodium  phosphate, 
and  set  aside  for  eight  or  ten  hours  in  order  that  the  magnesia  may 
separate  out  as  NHjMgPO^.GH.^O.  Wash  this  precipitate  on  to 
a  filter  with  ammonia  solution.  Dry  in  hot-air  chamber  and  ignite 
to  form  Mg2P207,  from  which  the  weight  of  MgO  is  easily  calculated. 
Or  the  ammonio-magnesium  phosphate  precipitate  may  be  brought 
upon  a  filter  washed  with  ammoniacal  water  in  the  cold,  dissolved 
in  acetic  acid,  and  titrated  with  standard  uranium  solution,  each 
c.c.  of  which  represents  0'0028i5  gramme  magnesia. 

The  phosphoric  acid  in  soils  is  determined  as  follows :  (i)  Incinerate 
and  digest  a  weighed  quantity  of  the  soil  with  HCl,  evaporate  to 
dr}-ness  to  render  silica  insoluble,  redigest  with  acid,  filter,  and  wash. 
(2)  Concentrate  the  filtrate  and  washings  to  small  bulk  and  add 
excess  of  ammonium  molybdate  in  nitric  acid,  stand  aside  in  a  warm 
place  for  two  days,  decant  the  liquid  through  a  filter,  wash  the  pre- 
cipitate several  times  by  decantation  first  with  dilute  HNO3,  and 
afterwards  with  small  amounts  of  distilled  water,  then  transfer  it 
to  the  filter  and  wash  free  from  excess  of  acid,  dissolve  the  am- 
monium-phospho-molybdate  in  ammonia,  add  magnesium  mixture, 
filter,  wash,  dry,  and  ignite  the  precipitate,  ^^'eigh  the  resulting 
Mg2P207,  from  which  calculate  the  P2O5. 

Or  the  method  described  for  magnesia  may  be  used,  wherein  the 
ammonio-magnesium  phosphate  precipitate  is  dissolved  in  acetic 


SOIL  109 

acid,  and  titrated  with  standard  uranium  acetate  or  nitrate  solution, 
each  c.c.  of  which  equals  0-005  gramme  P2O5. 

The  total  organic  nitrogen  of  soil  is  best  estimated  by  Kjcddahl's 
method.  The  ammonia  resulting  from  the  distillation  of  the  am- 
monium sulphate  with  excess  of  KOH  is  received  in  j^  or  -^^  H2SO4. 
At  the  end  of  the  distillation  the  standard  H2SO4  remaining  is  titrated 
with  standard  alkali,  and  the  ammonia  absorbed  by  the  acid  calcu- 
lated.    The  N  forms  \y  by  weight  of  the  NH3. 

Where  total  N  (including  HNO2  and  HNO3)  is  required  the  oxidized 
N  must  first  be  converted  into  NH3  by  boiling  with  Al  and  NaOH, 
or  by  the  action  of  the  Cu-Zn  couple. 

Clay  and  humus  are  the  two  most  important  ingredients  of  soils. 
The  plasticity  and  adhesiveness  of  clay,  together  with  the  fineness 
of  the  particles,  serve  to  hold  together  various  other  aggregates  of 
soil.  The  extreme  fineness  of  the  particles  of  clay  causes  it  to  retain 
water,  solids  dissolved  in  water,  and  gases. 

If  by  plastic  or  colloidal  clay  be  understood  the  particles  of  soil 
under  o -01  millimetre  diameter  which  remain  suspended  in  a  column 
of  water  eight  inches  high  for  twenty-four  hours,  soils  may  be  divided 
into  the  following  six  classes : 

Very  sandy  soils  containing  up  to  3      per  cent.  clay. 

Sandy  ,,  ,,  ,,      3-10 

Sandy  loams  ,,  ,,    10-15 

Clay         „  „  „    15-25 

Clay  soils  ,,  ,,    25-35        ,, 

Heavy  clays  ,,  ,,    35-45        ,,  ,,  and  over. 

Admixture  of  fine  powders,  such  as  Ca(0H)2  and  Fe2(OH)6 
diminish  greatly  the  adhesiveness  of  clay,  caused  by  the  hydrated 
silicates. 

'  Humus  '  or  '  vegetable  mould  '  is  formed  by  the  decomposition 
of  organic  matter,  largely  cellulose,  derived  from  the  roots,  stems, 
and  leaves  of  plants.  Its  accumulation  near  the  surface  is  natural, 
and  it  distinguishes  soil  from  subsoil.  Its  production  is  controlled 
by  moisture,  oxygen,  temperature,  and  micro-organisms.  With  a 
low  temperature  and  as  much  water  as  will  shut  out  air  the  organisms 
that  transform  vegetable  tissue  into  humus  are  bacteria;  but  the 
disinfectant  compounds  produced  soon  kill  the  bacteria,  and  the 
process  remains  henceforth  a  slow  and  purely  chemical  one.      In 


no  PRACTICAL  SANITARY  SCIENCE 

the  solid  brown  decomposition  products  formed  in  peat  are  found 
ulmic  and  apocrcnic  acids  soluble  in  caustic  and  carbonated  alkalies, 
and  fonuing  insoluble  salts  with  the  earths  and  metals,  and  ulmin, 
insoluble  in  alkalies  but  after^vards  soluble  on  oxidation.  CO.,  and 
CH4  are  formed  in  large  quantities  under  these  conditions.  Pro- 
longed cultivation  of  soils  tends  to  production  of  acids;  hence  the 
advantages  of  calcareous  formations.  In  the  presence  of  earthy 
carbonate,  especially  that  of  lime,  which  neutralizes  acids  as  formed, 
moderate  degrees  of  moisture,  and  free  circulation  of  air,  humification 
proceeds  under  the  influence  of  moulds  instead  of  bacteria.  0  and 
H  are  eliminated  as  CO.,  and  HoO,  and  an  increase  takes  place  in  the 
percentage  of  C  and  X.  When  humification  is  complete  and 
oxidation  proceeds,  the  X  may  rise  to  high  figures,  portions  being 
wholly  oxidized  to  nitrates. 

Humus  is  highly  porous,  absorbs  water  and  gases,  and  is  gradually 
oxidized  by  bacteria.  The  measure  of  this  oxidation  can  be  gauged 
by  the  amount  of  CO2  produced.  Humus  substances  are  gelatinous 
when  moist,  but  not  markedly  adhesi\'e  or  plastic.  The  densit)'  of 
humus  is  about  1-4  ;  hence  soils  rich  in  humus  are  light  (humus  is  the 
lightest  ingredient  of  soil)  when  compared  with  clay  and  sandy 
soils,  and  '  light  '  in  the  agricultural  sense  of  being  easily  tilled. 

The  X  of  humus  does  not  exist  in  the  form  of  XH3,  as  it  cannot  be 
set  free  by  treatment  in  the  cold  with  lime  or  alkalies.  When  humus 
is  boiled  with  lime  or  alkalies  ammonia  is  slowly  evolved  for  an 
indefinite  time,  but  the  whole  of  the  X  is  not  expelled.  Such  be- 
ha\dour,  together  with  its  slightly  acid  reaction,  points  to  humus 
being  of  the  nature  of  an  amido-compound. 

Hmnus  formed  from  sugar,  cellulose,  gums,  etc.,  combines  with 
ammonia  as  with  other  bases,  and  at  first  the  ammonia  can  be  readily 
expelled  from  this  as  from  other  ammonia  salts.  But  after  a  time 
the  amidic  condition  appears  to  be  assumed,  as  caustic  alkalies  act 
but  slowly,  and  are  unable  to  expel  the  whole  of  the  X.  These  facts 
are  of  importance  in  nature,  as  XH3,  generated  in  or  taken  up  by  the 
soil,  is  in  the  course  of  time  rendered  inert  and  unavailable  for  plants 
until  nitrification  has  been  effected. 

Humin  and  ulmin  found  in  the  deeper  layers  of  peat  are  in  process 
of  time  oxidized  into  humic  and  idmic  acids  capable  of  combining 
with   bases.      Further   oxidation   produces   crenic   and   apocrenic 


sou.  Ill 

acids,  readily  soluble  in  water  and  capable  of  uniting  with  Imsts  to 
form  salts.  These  acids  react  on  decomposable  silicates  and  dissolve 
them;  they  also  dissolve  ferric  hydrate.  In  this  way  rust-coloured 
soils  are  bleached  by  stagnant  water  and  deprived  of  much  of  their 
mineral  plant  food. 

In  ordinary  soils  humus  rarely  exceeds  5  per  cent.,  in  peat  and 
marsh  lands  it  may  reach  20  per  cent. 

Humus  may  be  estimated  by  extracting  the  soil  with  dilute  ricid 
to  set  free  the  humic  bodies  from  their  combinations  with  lime  and 
magnesia.  The  residue  is  then  extracted  with  moderately  dilute 
solutions  of  ammonia.  Evaporation  of  the  ammonia  extracts  leave 
the  humus  as  a  black  lustrous  substance  [matiere  ■noire  of  Grandeau). 
As  this  contains  a  variable  amount  of  ash  it  is  burnt  and  the  ash  is 
subtracted  from  the  first  weight. 

A  determination  of  the  ash  of  humus  gave : 


Insoluble  matter  (principally  silica)  - 

-     62-6 

K,0 

-       7-5 

Na,0 

-       8-1 

CaO 

o-i 

MgO 

-       0-3 

FeoOg 

-       3-1 

AlA 

-       3-4 

P2O5 

-     12-3 

SO3 

-       0-9 

CO, 

-       17 

lOO-O 

Bacteria  of  Soil. — Inseparably  correlated  with  humus  and  carbo- 
hydrates in  soil  are  varied  forms  of  bacteria.  More  than  40,000,000 
per  c.c.  have  been  found.  The  bulk  of  soil  bacteria  reside  near  the 
surface,  as  there  alone  are  to  be  found  the  conditions  necessary 
to  growth  and  multiplication.  The  best  foodstuffs  appear  to  be 
water,  proteins,  and  soluble  carbohydrates  derived  from  deca5'ing 
plants,  stable  manure,  etc.  When  the  decaying  matter  reaches  the 
stage  of  humus,  only  few  bacteria  remain.  The  most  important 
functions  of  soil  bacteria  are  related  to  putrefaction,  nitrification, 
denitrification,  and  nitrogen-fixation. 

Most  of  the  putrefactive  bacteria  are  concerned  with  the  breaking 
down  of  complex  protein  matter,  with  evolution  of  NHg,  and  fonna- 


112  PRACTICAL  SAXITARY  SCIENCE 

tion  of  ammonium  salts.  Common  examples  of  soil  organisms  of 
this  type  are — Bacillus  mycoides,  B.  suhtilis,  B.  mesentericus  vidgatus, 
Proteus  vulgaris,  P.  zenkcri,  Bacillus  coli,  B.  putrificus,  B.  lactis  aero- 
genes,  B.  fiuorescens  liqiiefaciens,  streptococci,  etc.  In  acid  soils 
rich  in  humus  certain  fungi  such  as  Peniri Ilium  glaucum,  Mucor 
mucedo,  and  species  of  Botrytis  and  Torula  accomplish  the  cleavage 
of  proteins. 

Nitrification  is  carried  out  in  two  stages:  ammonium  compounds 
are  oxidized  to  nitrites  by  such  organisms  as  Winogradsky  included 
in  the  genus  Nitrosoinoiias  curopcBa  ;  and  nitrites  are  oxidized  to 
nitrates  by  several  forms  included  in  the  genus  Nitrohacter.  The 
conditions  necessaiy  to  these  changes  are  definite.  In  addition  to 
nitrifiable  material  and  nitrifying  bacteria,  a  fairly  high  tempera- 
ture (24°  C),  a  moderate  degree  of  moisture,  free  access  of  oxygen, 
a  base  or  its  carbonate  with  which  the  acids  formed  in  the  process 
of  oxidation  can  imite,  free  CO.,,  and  darkness  are  essential.  In 
acid  soils  nitrification  ceases,  as  also  in  soils  in  which  the  bases  have 
become  fully  saturated.  Carbonates  of  lime  and  magnesia  are  the 
bases  most  favourable  to  nitrification,  and  excess  of  these  produces 
no  injury.  The  amounts  of  carbonates  of  potash  and  soda  must  be 
strictty  limited.  The  nitrifying  organisms  are  strictly  aerobic;  in 
non-porous  or  water-logged  soils  they  quickly  die  out.  They  derive 
their  carbon  from  CO2,  as  when  cultivated  in  the  presence  of 
carbonates  in  an  atmosphere  washed  with  KOH  they  fail  to 
develop. 

Various  denitrifying  bacteria  have  recently  been  studied.  One 
of  the  most  effective  organisms  is  Burri's  B.  denitrificans,  found  on 
the  surface  of  old  straw  and  in  fiesh  horse-dung.  If  some  fresh 
hcrse-dung  be  placed  in  a  close-flask  containing  KNO.5,  nitrogen 
and  carbon  dioxide  are  evolved,  and  in  a  few  days  the  nitrate  has 
disappeared.  B.  hutyricus,  which  in  the  absence  of  easily  reducible 
compounds  evolves  free  nitrogen,  reduces  nitrates  to  nitrites,  and 
also  forms  NH3  by  addition  of  H  to  N  just  set  free  by  reduction. 
B.  mycoides  forms  ammonia  from  antecedent  proteins,  and  also 
reduces  nitrates  to  nitrites  and  ammonia.  Reduction  may  be  to 
nitrites,  and  no  further;  it  may  go  on  to  ammonia;  nitrates  and 
nitrites  may  be  reduced  with  evolution  of  NO  and  N2O;  and,  finally, 
nitrates  and  nitrites  may  be  reduced  with  production  of  free  N.     A 


SOIL  113 


large  number  of  bacteria  found  in  faecal  matter,  water,  and  soil 
decompose  nitrates  with  evolution  of  free  N. 

The  reactions  between  nitrates  undergoing  denitrification  and 
organic  carbon  compounds  may  be  represented  by  the  equations: 

C +2NaN0.j=  CO2 +2NaN02 
C  +  2NaN02  =  N2O  +  NaX03 
C+2N20=2N2  +  C02, 

where  C  represents  the  oxidizable  carbon  of  the  carbon  compounds. 

An  important  group  of  soil  bacteria  is  found  in  connection  with 
the  root  nodules  of  leguminous  plants. 

The  mode  of  supply  of  nitrogen  to  plants  was  long  a  subject  of 
debate.  Liebig  thought  that  it  was  derived  from  the  ammonia  in 
rain  water.  Boussmgault  proved  that  plants  do  not  take  N  directly 
from  the  air.  Lawes  and  Gilbert  confirmed  Boussingault's  con- 
clusions. Hellriegel  and  Wilfarth  pointed  out  that  the  tubercles 
on  the  roots  of  leguminous  plants  are  produced  by  bacilli  which 
absorb  free  N  from  the  air,  and  pass  it  over  to  the  host.  Beyerinck 
later  separated  and  described  the  B.  radicicola. 

The  tissues  of  one  of  these  nodules  on  microscopic  examination 
are  found  to  contain  a  number  of  free  motile  bacteria,  and  a  niunber 
of  quiescent  forms  much  larger  in  size.  When  the  nodule  has 
reached  full  size,  the  large  quiescent  bacteria  begin  to  collapse,  and 
part  with  their  nitrogenous  substance.  Later  the  shells  drop  off 
and  carry  minute  bacteria  into  the  soil,  which  in  due  course  again 
become  active.  The  nodules  adhere  but  loosely  to  the  roots.  The 
ease  with  which  they  may  fall  off  doubtless  accounts  for  the  diffi- 
culty experienced  in  transplanting  legumes. 

The  nodules  above  mentioned  vary  in  shape  and  size,  according 
to  the  species  of  leguminous  plant  to  which  they  are  attached,  and 
are  caused  by  the  Bacillus  or  Pseudomonas  radicicola  (Beyerinck) 
penetrating  the  root  hairs.  On  entering  root  hairs  the  organism 
develops  and  forms  a  thread-like  zooglea  technically  known  as  the 
'  infection  thread,'  which  resembles  the  hyphaof  a  fungus,  and  which 
excites  the  neighbouring  cells  of  the  rootlet  to  rapid  multiplication 
and  the  formation  of  the  nodule.  In  the  infection  threads  and 
youngest  nodules  the  organisms  are  straight  rods.  In  older  parts 
they  are  branched  and  curved,  and  are  known  as  bacteroids  which 


114  PRACTICAL  SANITARY  SCIENCE 

have  lost  their  power  of  di\ision :  Liter  tliey  are  digested  by  a  ])roteo- 
lytic  enzyme  secreted  b}'  the  protoplasm  of  the  root.  The  digested 
substances  pass  to  the  flowers  and  seeds  of  the  ripening  plant.  N- 
fixation  reaches  a  maximum  at  the  time  when  the  plants  begin  to 
flower.  When  the  crop  is  har\-ested,  a  large  sur})lus  of  nitrogen  is 
left  behind  in  the  nodules  in  the  soil. 

Other  bacteria  are  known  to  absorb  fice  N,  of  which  may  be 
mentioned  Winogradski's  Clostridium  pastorianum  and  Beyerinck's 
Azotobacter. 

The  nitrogen-fixing  powers  of  soil  may  be  determined  by  esti- 
mating the  total  N  in,  say,  200  grammes  of  soil,  and  repeating  the 
experiment  after  six  weeks'  incubation  at  20°  C  in  a  solution 
composed  of  grape  sugar  40  grammes,  K2HPO4  2  grammes,  NaCl 
2  grammes,  CaCO.,  10  grammes,  and  water  2  litres. 

The  nitrifying  and  denitrifying  powers  of  soils  can  be  estimated 
in  the  same  manner  by  adding  known  quantities  of  ammonium  salts, 
nitrites,  and  nitrates,  respective!}',  to  a  suitable  inorganic  medium 
containing  a  soluble  carbohydrate. 

When  the  surface  soil  is  wetted,  moisture  may  rise  toward  the 
surface  from  the  lower  layers ;  this  is  probably  due  to  evaporation 
from  below,  followed  by  recondensation  by  the  cool  wetted  layer. 
The  condition  is  of  some  practical  interest,  inasmuch  as  cold  rain 
on  the  surface  may  raise  water  from  below. 

The  downward  percolation  of  water  is  most  rapid  in  those  soils 
in  which  capillary  ascent  is  quickest — i.e.,  in  coarse  sand. 

The  rapidity  of  percolation  decreases  as  the  wetted  soil  column 
increases  in  depth;  as  the  wetted  column  lengthens,  the  frictional 
resistance  increasingly  opposes  the  effects  of  the  hydrostatic  pressure 
from  above  until  downward  movement  becomes  little  more  than 
lateral  movement  or  capillary  ascent  from  below.  The  frictional 
resistance  has  counteracted  gravity  to  such  a  degree  that  the  capil- 
lary coefficients  of  the  soil  become  the  governing  factors  of  the 
water  movement. 

It  is  often  desirable  to  protect  a  soil  from  excessive  evaporation 
in  order  either  to  prevent  lowering  of  temperature  or  to  save  vegeta- 
tion in  time  of  drought.  The  preparation  by  tilth  of  a  layer  of  loose 
dry  surface  soil  is  the  best  means  of  securing  this  object.  It  would 
appear  on  first  sight  that  such  a  soil  admits  of  leady  access  of  air, 


SOIL  115 

and  therefore  of  evaporation;  whilst  this  is  true,  it  is  equally  true 
that  the  coarse  particles  are  incapable  of  withdrawing  moisture  from 
the  denser  layers  beneath  in  the  same  manner  as  a  dry  sponge  is 
incapable  of  withdrawing  moisture  from  a  wet  brick,  notwithstanding 
the  fact  that  a  dry  brick  will  readily  absorb  all  the  water  from  the 
relatively  large  pores  of  a  wet  sponge. 

The  disinfectant  action  of  dry  soil  and  its  capacity  for  absorbing 
offensive  gases  have  long  been  known.  The  decoloriziation  by  soil 
of  drainage  from  manure-heaps,  dye-works,  and  tanneries,  and  the 
filtration  of  drinking  waters  on  the  large  scale  by  fine  sand,  are 
equally  familiar.  It  should  not  be  forgotten,  however,  that  these 
powers  are  strictly  limited.  Dry  soils  are  powerful  gas-absorbers, 
and  peat  appears  to  excel  all  others  in  this  property. 

The  temperature  of  the  soil  is  derived  from  the  sun's  rays, 
chemical  changes  in  the  soil,  and  from  the  heat  of  the  earth's 
interior.  The  first  of  these  is  the  chief  factor  in  influencing  tem- 
perature. The  more  perpendicularly  the  rays  strike  the  soil  the 
greater  the  amount  of  heat  received. 

The  colour,  composition,  moisture,  and  compactness  of  the  soil 
influence  the  temperature.  A  black  surface  absorbs  heat  rays  more 
than  a  white  one.  Snow  melts  more  rapidly  when  covered  with 
soot. 

Sands  and  mineral  substances  in  general  conduct  heat  better  than 
water,  air,  or  organic  matter.  Organic  matter  is  a  poor  conductor 
of  heat ;  hence  the  more  humus  a  soil  contains  the  more  slowly  will 
it  respond  to  the  action  of  the  sun.  Moisture  influences  soil  tem- 
perature through  the  high  specific  heat  of  water  and  through  the 
disappearance-  of  heat  due  to  evaporation.  The  specific  heat  of 
ordinary  dry  soils  is  about  one-fifth  that  of  water.  The  drier  a  soil, 
the  less  the  evaporation  and  the  greater  its  warmth. 

Veg-etation  protects  against  excessive  heating  in  hot  climates, 
and  loss  of  heat  in  cold  climates.  Trees  impede  wind  currents  and 
obstruct  the  sun's  rays,  so  that  less  loss  of  moisture  occurs  by 
evaporation.  It  may  be  quite  calm  in  the  centre  of  a  wood  whilst 
a  gale  blows  outside. 

A  soil  in  which  the  ground-water  is  high — say  5  to  10  feet  from 
the  surface — has  long  been  regarded  as  unfavourable  to  health. 
Such  a  soil  renders  the  atmosphere  damp,  and  appears  to  conduce 


Ii6  PRACTICAL  SAXITARY  SCIENCE 

to  rheumatism  and  diseases  of  the  respiratory  tract.  Lowering  of 
the  gronnd-\vater  le\-el  by  drainage  has  largel}-  inipro\-ed  the  health 
conditions  of  man\-  soils.  Soil  dampness  appears  to  be  connected 
with  pulmonar\"  tuberculosis. 

T\phoid  fever,  cholera,  dysenteries,  and  other  intestinal  maladies 
have  been  etiologically  related  by  various  observers  to  soil,  ground- 
air,  and  ground- water :  it  is  probable  that  each  and  all  of  these  act 
as  media  of  conveyance  of  the  specific  micro-organisms  of  these 
diseases. 

Newsholrne  regards  epidemics  of  diphtheria  as  intimately  related 
to  dry  years,  and  holds  that  they  do  not  occur  when  the  rainfall  is 
above  the  average. 

Malaria  is  connected  with  soil  conditions  in  the  breeding  of  the 
specific  mosquitoes. 

Ankylostomiasis  or  uncinariasis  is  intimatel}'  connected  with  the 
soil,  in  that  the  eggs  of  the  parasite  Ankylostomnm  duodenale  escape 
with  the  faeces  and  are  deposited  in  the  soil,  where  they  hatch  in 
twenty-four  hours.  The  embryos  shed  their  skin  twice,  and  after 
a  few  weeks  are  ready  to  infest  man.  The  chief  portal  of  infection 
is  the  mouth.  Several  observers  assert  that  the  parasites  can  reach 
the  intestine  through  the  skin. 

The  various  theories  which  connected  goitre  with  particular  con- 
stituents of  the  soil,  such  as  metallic  sulphides,  magnesian  limestone, 
etc.,  are  now  practically  abandoned. 

Bactepiologrical  Examination  of  Soil — This  examination  is  of 
service  principally  in  connection  with  water-supplies,  more  especially 
contamination  of  water  by  surface  washings.  Much  work  has  been 
done  on  B.  typhosus  in  soils,  and  findings  have  been  very  varied. 
Under  favourable  conditions  it  appears  that  this  organism  can 
survive  for  a  considerable  time. 

The  organisms  of  tetanus  and  malignant  oedema  are  widely  dis- 
tributed in  cultivated  soil.  They  are  isolated  anaerobically  from 
small  quantities  of  soil  or  soil  washings  in  the  usual  way.  Advan- 
tage is  taken  of  the  fact  that  their  spores  survive  heating  at  80°  C 
for  a  quarter  of  an  hour,  when  all  non-sporing  organisms  are  de- 
stroyed. These  spores  are  grown  on  various  media  over  alkaline 
pyrogallic  solution,  and  the  ;growths  investigated  in  the  usual 
manner. 


SOIL  117 

In  collecting  soil  for  examination,  the  depth  from  which  the 
material  is  to  be  recovered  having  been  decided  upon,  a  sterile  instru- 
ment is  used  for  procuring  six  to  twelve  specimens,  which  are  mixed 
in  order  to  produce  an  average  sample.  This  is  carried  to  the 
laboratory  in  a  sterile  vessel. 

A  gramme  is  shaken  up  in  100  c.c.  sterile  water  in  a  sterile  flask, 
and  from  this  dilutions  are  made— i  c.c.  of  this  solution  is  trans- 
ferred to  100  c.c.  sterile  water  in  a  second  flask,  etc. 

Quantitative  and  qualitative  estimations  of  B.  coli,  streptococci, 
and  B.  enteritidis  sporogenes  are  carried  out  in  these  liquid  prepara- 
tions in  the  same  manner  as  in  dealing  with  water. 

B.  coli  is  absent  from  un  contaminated  soils,  or  present  in  very 
small  numbers  only.  Houston  finds  that  it  is  not  readily  isolated 
even  from  polluted  soils  unless  the  contamination  is  recent  and 
large  in  amount.  He  considers  the  spores  of  B.  enteritidis  sporogenes 
indicative  of  contamination,  but  not  necessarily  recent.  Strepto- 
cocci are  found  in  minimum  quantities  of  soil  recently  polluted  with 
sewage.     They  disappear  extremely  rapidly. 


CHAPTER    X 

AIR 

The  air  is  a  mechanical  mixture  of  gases.  One  hundred  volumes 
contain,  roughly,  21  of  oxygen,  78  of  nitrogen,  and  i  of  argon, 
krypton,  heliimi,  neon,  zeon,  and  carbon  dioxide. 

A  distinguishing  property  of  gases  is  that  a  mass  of  gas  introduced 
into  a  closed  vessel  alwaj^s  completely  fills  the  vessel,  however  large. 
Consider  two  vessels  of  eiqual  volume  connected  by  a  tube  carrying 
a  tap,  and  let  one  of  these  vessels  be  filled  with  a  gas  and  the  other 
exhausted;  on  opening  the  tap,  the  gas  rushes  into  the  exhausted 
vessel  until  the  same  quantity  of  gas  exists  in  each  vessel.  Close 
the  tap,  and  once  more  exhaust  one  of  the  vessels;  on  opening  the 
tap,  the  gas  expands  and  again  fills  equall}'  the  two  vessels.  The 
operation  may  be  repeated  indefinitely,  and  the  gas  will  always 
exert  some  pressure  on  the  inside  of  the  containing  vessel. 

The  density  of  a  gas,  like  the  densit}'  of  any  other  body,  is  the 
mass  of  unit  volume,  and  is  sometimes  referred  to  hydrogen  and 
sometimes  to  air  as  unity  at  0°  C,  and  under  a  pressure  of  one 
standard  atmosphere. 

The  only  elasticity  of  which  a  gas  is  capable  is  that  of  volume  or 
bulk,  since  it  is  alone  to  a  change  of  volume  that  a  gas  offers  any 
permanent  resistance. 

If  the  pressure  on  volume  V  of  a  gas  be  increased  from  F  toF  +p, 
and  as  a  consequence  the  volume  be  reduced  from  V  to  V  —  v,  the 
temperature   remaining   constant,    then   the   strain   produced   in 

V 

voliune  V  is  v,  and  per  unit  volume  y,  and  the  corresponding  stress 

is  p.     Therefore,  since  the  elasticity  of  a  body  is  the  ratio  of  the 

V  V 

stress  to  the  strain,  the  elasticity  of  the  gas  is  />  -^y,  or  />- . 

By  compressing  air  with  mercury  in  a  U-tube  closed  at  one  end, 

118 


AIR  fil9 

Robert  Boyle  found  a  series  of  values  for  the  volume  of  a  given  mass 
of  air  under  different  pressures,  and  he  enunciated  in  1662  a  law 
known  by  his  name — viz.,  that  (the  temperature  remaining  un- 
changed) PV=  constant.  Mariotte  fourteen  years  later  enunciated 
the  same  law. 

That  all  gases  have  the  same  coefficient  of  thermal  expansion  was 
first  enunciated  by  Charles.  Consider  a  mass  of  gas  of  volume  Vq  at 
pressure  pQ,  and  imagine  its  volume  kept  constant  while  its  tempera- 
ture is  lowered  from  0°  C.  to  - 1°,  the  pressure  p  will  by  Charles's  law 

be  given  by 

p=Po{i~at), 

where  a  is  the  coefficient  of  expansion.     If  the  cooling  be  continued 

-1° 
to  a  temperature  ~^> 

P=Pq{i~i)  =  o, 

i.e.,  at  this  temperature  the  gas  would  exert  no  pressure  on  the 
walls  of  the  containing  vessel.  According  to  the  kinetic  theory  of 
gases,  this  can  only  occur  when  the  velocity  of  translation  of  the 
molecules  is  2;ero.  This  temperature  is  called  the  absolute  zero.  ' 
Taking  a  as  o-yrr  (the  mean  value  for  hydrogen  between  0°  and 
100°  C),  the  absolute  2;ero  will  be  -273°  C.  In  order  to  convert 
temperatures  referred  to  0°  C.  to  the  corresponding  temperatures 
referred  to  the  absolute  zero,  it  is  only  necessary  to  add  273.  If  T 
and  t  represent  respectively  the  absolute  and  the  ordinary  tempera- 
ture, •■ 

T=^  +  273. 

By  Charles's  law — • 

p=PQ{i+at), 
and  v=Vo{i+ at), 

substituting  for  a  its  numerical  value, 

-PJl 
-  273'  .    , 

and.=  -. 


120  PRACTICAL  SANITARY  SCIENCE 

At  any  other  temperature  T^,  if  when  the  volume  is  constant  the 
pressure  is  />\  and  when  the  pressure  is  constant  the  volume  is  v^ 

273 ' 

273 
..     ^1-^1,  ana  ^^i-;j-i. 

or  the  pressure  at  constant  volume  varies  directly  as  the  absolute 
temperature,  and  the  volume  at  constant  pressure  varies  directly 
as  the  absolute  temperature. 

A  Barometer  is  an  instrument  used  for  measuring  the  pressure 
exerted  by  the  atmosphere.  Barometers  may  be  divided  into  two 
classes:  (i)  Those  in  which  the  pressure  is  measured  in  terms  of  the 
height  of  a  column  of  a  liquid;  (2)  aneroid  barometers,  in  which  the 
pressure  is  measured  b}-  the  strain  produced  in  the  lid  of  a  metal  box. 

Mercury  is  practically  always  used  in  liquid  barometers  on  account 
of  its  great  density  rendering  the  height  of  the  column  supported 
by  the  atmosphere  a  convenient  quantity  with  wliich  to  work. 
Further,  mercury  does  not,  as  does  glycerin,  absorb  moisture  from  the 
air ;  it  has  a  fairly  low  freezing-point,  and  a  high  boiling-point. 

The  simplest  fonn  of  barometer  is  the  siphon  barometer,  consisting 
of  a  U-tube,  the  longer  limb  (86  centimetres)  of  which  is  closed  while 
the  shorter  is  open.  The  tube  is  filled  with  mercury;  by  boiling  the 
mercury  any  air  or  moisture  adhering  to  the  mercury  or  bore  of  the 
tube  is  expelled.  The  distance  between  the  levels  of  the  mercury  in 
the  two  limbs  is  the  barometric  height.  When  the  pressure  in- 
creases, the  mercury  falls  in  the  open  limb  and  rises  in  the  closed  by 
the  same  amount,  so  that  the  difference  of  level  is  double  the  rise  in 
the  closed  end  or  fall  in  the  open.  If  a  scale  be  attached  to  either 
tube,  and  each  inch  or  centimetre,  as  the  case  may  be,  be  marked 
half  an  inch  or  centimetre,  the  reading  at  once  gives  the  height  of  the 
barometer. 

In  the  Fortin  barometer  the  scale  is  graduated  in  inches  to  0-05, 
and  the  vernier  usually  reads  to  0-002  inch.  The  cistern  is  closed 
below  by  a  leather  bag  protected  by  a  metal  sheath,  into  the  bottom 
of  which  is  fitted  a  screw  for  the  requisite  adjustments.     Having 


AIR 


taken  the  temperature  by  the  attached  therm.omctcr,  the  mercury 
in  the  cistern  is  raised  or  lowered  by  the  screw  until  the  ivory  point 
(fiducial  point)  or  zero  of  the  scale  and  its  reflected  image  in  the 
mercury  are  just  in  contact;  the  vernier  is  then  moved  by  the  upper 
milled  head  until  its  lower  edge  just  excludes  the  light  from  the  top 
of  the  mercurial  column;  the  reading  is 
then  made  from  the  scale  and  vernier. 

Verniers  are  of   different   lengths,  and 
contain  variable  numbers  of  divisions.     A  I —    3  7 

common  form  is  i^  inches  long,  divided 
into  twenty-five  parts,  which  correspond 
in  length  with  twent3/-four  divisions  of 
the  principal  scale. 

A  division  on  the  principal  scale  is  there- 
fore greater  than  one  on  the  vernier  by 


(~  X  i^  inches)  —  (ttV  x  li  inches) 

=  -^ — -  X  1-2  inches 
6oo 

=  0-002  inch. 


(J 


To  read  the  vernier  adjust  its  lower  edge 
with  the  top  of  the  meniscus,  when  two 
very  small  triangles  of  light  will] appear, 
one  on  either  side.  If  the  lower  edge  of 
the  vernier  correspond  with  a  division  of 
the  principal  scale,  this  is  the  reading; 
but  if  not,  it  is  evident  that  the  interval 
between  the  surface  of  the  mercury]  and 
the  division  of  the'  principal  scale  next 
below  is  equal  to  the^difference  between 
the  lengths  of  the  divisions  of  the  vernier 
and  principal  scales  (o-oo2  inch)  multiplied 

by  the  number  of  vernier  divisions  which  intervene  between  the 
lower  edge  (zero  of  vernier)  and  that  division  which  exactly  corre- 
sponds with  a  division  on  the  principal  scale. 

Suppose  in  a  given  example  that  the  lower  edge  of  the  vernier 
cuts  the  principal  scale  between  29-15  and  29-2  inches,  and  when  the 
vernier  scale  is  examined  it  is  found  that  its  thirteenth  division 


20- 


15- 


10- 


30 


S.9 


Fig.  24. 


122  PRACTICAL  SAXITARY  SCFEMCE 

corresponds  with   a  division  of   the  principal  scale,  the   reading 
will  be : 

29-15  inches  + 13  X  0-002  inches 

=  29-15  inches +  0-026  inch 

=  29-176  inches. 

The  Kew  barometer,  originally  invented  by  Adic  for  use  at  sea, 
has  a  closed  iron  cistern,  and  scale  of  contracted  inches.  The  tube 
is  of  small  calibre  throughout,  in  order  to  lessen  the  oscillations  of  the 
mercury  by  the  ship's  motion  (known  as  '  pumping  ').  A  small 
aperture,  covered  with  leather,  in  the  roof  of  the  cistern,  allows 
atmospheric  pressure  to  exert  itself  on  the  contained  mercury. 
Fitzroy's  gun  barometer  is  a  modification  of  the  Kew. 

Hooke's  wheel  barometer  is  a  siphon  barometer.  On  the  surface 
of  the  mercury  in  the  lower  limb  is  a  float  carrying  a  needle  indicator, 
which  moves  on  a  graduated  circular  dial. 

Various  self-recording  barographs  are  on  the  market,  records 
being  obtained  mechanically,  photographically,  and  electrically. 

In  order  to  make  an  observation  of  the  barometer  comparable 
with  other  observations  taken  at  other  times  and  places,  certain 
corrections  must  be  applied  to  it ;  some  of  these  refer  to  an  individual 
instrument,  and  others  to  all  readings  of  any  instrument.  Of  the 
former  class  there  are  three — corrections  for  index  error,  capacity, 
and  capillarity.  Of  the  latter  class  there  are  also  three — corrections 
for  temperature,  altitude,  and  gravity. 

The  index  error  is  made  by  the  workman  who  laid  off  the  scale  of 
the  instrument.  It  is  discovered  when  the  instrument  is  verified  at 
Kew  or  elsewhere.  Correction  for  capacity  depends  on  the  propor- 
tion borne  by  the  sectional  area  of  the  tube  to  that  of  the  cistern. 
At  one  point  of  the  scale  the  reading  is  correct ;  when  the  mercury  is 
above  that  point  the  correction  is  additive,  when  below  subtractive. 

Capillaritv  between  glass  and  mercury  tends  to  depress  the 
mercury,  and  in  larger  degree  the  smaller  the  tube;  it  is  also  greater 
in  an  '  unboiled  '  than  in  a  '  boiled  '  tube.  All  certificates  from 
Kew  for  '  Kew  '  pattern  barometers  give  a  correction  at  each  ^  inch, 
including  the  above  three  corrections. 

Corrections  independent  of  the  Special  Instrument.— r^m- 
perature. — If  the  scale  by  means  of  which  the  height  of  the  column  is 
measured  be  correct  at  0°  C,  then  at  all  temperatures  above  0°  the 
length  of  the  divisions  will  be  too  great,  since  all  metals  increase  in 


AIR  123 

length  when  heated.  Let  a  be  the  coefficient  of  h"near  expansion  of 
the  metal  of  which  the  scale  is  made,  so  that  unit  length  of  the  scale  at 
0°  C.  becomes  i+at  at  t°  C  If  ht  is  the  reading  at  temperature  t, 
then  the  height  as  measured  with  the  scale  at  0''-'  would  be  greater, 
since  the  length  of  each  division  of  the  scale  would  be  less  in  the  ratio 
of  I  to  I  +at,  so  that  the  number  of  divisions  corresponding  to  a 
given  length  (length  of  mercury  column)  will  be  increased  in  the 
ratio  T+ at  to  i. 

If  Hq  be  the  barometer  reading  corrected  for  expansion  of  the 
scale,  hQ=  ]\t{i  +  at).  But  h^  is  the  height  of  a  column  of  mercury  at 
temperature  t,  and  the  problem  is  to  find  what  the  height  would  be  if 
the  temperature  were  0°  C.  If  dt  be  the  density  of  mercury  at  t°,-dQ 
the  density  at  0°,  S  the  coefficient  of  cubical  expansion  of  mercury, 
and  H  the  height  which  the  column  would  have  if  the  mercury  stood 
at  0°  C.,  then  i  c.c.  of  mercury  at  0°  becomes  i  +S  c.c.  at  1°,  and 
I  +  S^  c.c.  at  t°.  Since  the  mass  M  of  the  mercury  remains  unchanged 
M=  Uo^o=  ''^i^i'  where  Vq  and  V<=  volumes  of  mass  M  at  tempera- 
tures 0°  and  t°  respectively. 

Since  S  is  excessively  small,  its  second  and  higher  powers  may  be 

neglected,  and  j  =r—U. 

Since  the  height  of  a  column  of  liquid  supported  by  a  given 
pressure  is  inversely  proportional  to  the  density, 

B.     dt  .^ 

.-.     Y{=h^[i-U)^ht{T-+at)  {i~8t)=Iit{i-{8~a)t), 
if  8at^,  which  is  excessively  small,  be  neglected. 

For  mercury,  8  =  0-000182;  for  brass,  a  =0-00002. 

Therefore,  for  a  mercury  barometer  with  a  brass  scale,  the  corrected 
height  corresponding  to  an  observed  height  ht  at  temperature  t°  C., 
is  given  by  H=;^.(i- 0-000162/). 

Altitude  and  Gravity. — If  g  =  acceleration  of  gravity  at  place  of 
observation,  and  ^45  that  at  latitude  45°  and  at  sea-level,  /=  latitude 
of  observation,  and/=  height  above  sea-level, 

=  1—0-0026  cos  2^  —  0 •0000002/". 


124  PRACTICAL  SANITARY  SCIENCE 

If  Hq  be  the  height  under  standard  conditions  corresponding  to 
the  same  pressure  as  does  H  at  the  place  of  observation, 

Hg=Hog'45;  orHo=     '^  =  /i/(i -o-oooi62/)(i  — 0-0026  cos 

b45 
2^—0-0000002/). 

If  a  bubble  of  air  be  passed  into  the  vacuum  of  a  barometer,  the 
mercury  falls;  if  several  bubbles  be  passed  in,  each  produces  a  de- 
pression. If  instead  of  air  a  drop  of  ether  be  introduced,  the 
mercury  also  falls  and  the  ether  becomes  complete^  vaporized,  even 
at  a  temperature  much  below  its  ordinary  boiling-point.  If  suc- 
cessive drops  of  ether  be  introduced,  it  will  be  found  after  a  time  that 
further  addition  of  ether  fails  to  produce  further  depression,  and 
that  the  ether  does  not  vaporize,  but  floats  on  the  top  of  the  mercury. 
Now,  if  the  space  above  the  mercury  be  enlarged  or  diminished  by 
raising  or  lowering  the  barometer-tube  in  the  cistern,  it  will  be  found 
that  so  long  as  any  liquid  ether  remains,  the  height  of  the  mercury 
column  is  constant,  but  that  the  amount  of  ether  which  vaporizes 
varies  with  the  space  above  the  mercur}'.  If  the  temperature  be 
increased,  more  ether  vaporizes,  and  the  mercury  column  becomes 
more  depressed.  The  vapour  exerts  a  pressure  which  partly  balances 
the  pressure  of  the  atmosphere.  The  depression  of  the  mercury 
measures  this  vapour  pressure.  When  excess  of  liquid  is  present,  so 
that  the  vapour  exerts  its  maximum  pressure,  the  vapour  is  said  to 
be  saturated.  If,  on  the  other  hand,  more  liquid  would  vaporize  on 
introduction  to  the  vacuum  the  vapour  is  said  to  be  unsaturated  or 
superheated.  The  vapour  pressure,  or  tension  of  a  liquid,  depends  on 
temperature  only.  Xon-saturated  vapours  obey  Boyle's  and 
Charles's  laws  only  approximately,  approximation  being  the  more 
complete  the  further  the  vapour  is  removed  from  its  saturation- 
point. 

Altitudes  are  calculated  from  barometric  readings  either  (i)  by 
Laplace's  formula,  or  (2)  by  Apjohn's  formula. 

Laplace's  formula  is — 

0=18,363  (log  P-log  p)     (i+"/ooo)' 
where  D=  difference  in  altitude  in  metres  of  the  two  stations. 
P=  barometric  pressure  in  mm.  Hg  at  lower  station. 
p=  ,,  ,,  ,,  ,,  higher 

/  =  temperature  in  "C.  at  lower  station. 
t' =  „  „  higher      „ 


AIR  125 

Apjohn's  formula  is: 

16,000  (P-/>)/       2t  +  t'\ 
^-        P  +  ^        ""V^  +  i.ooo^ 
where  D=  difference  in  altitude  in  metres  of  the  two  stations. 
P=  barometric  pressure  in  mm.  Hg  at  lower  station. 
p=  „  ,.  „  „  higher     „ 

t  =  temperature  in  °C.  at  lower  station. 
t'=  ,,  ,,  higher 

Thermometers. — The  freezing-point  of  a  thermometer  is  deter- 
mined by  surrounding  the  bulb  with  a  mixture  of  ice  and  distilled 
water.  The  boiling-point  is  fixed  by  suspending  the  instrument  in 
steam  issuing  from  water  boiling  at  a  pressure  of  760  mm.  of  Hg. 
The  tube  is  then  calibrated  between  these  two  points  into  100°  in  the 
Centigrade  instrument. 

Errors  of  Mercury  Thermometers. — ^The  observed  expansion  is 
really  the  difference  between  the  expansion  of  the  mercury  and  of 
the  glass  surrounding  the  mercury.  As  different  kinds  of  glass  do 
not  expand  exactly  alike,  thermometers  made  of  different  glasses  do 
not  completely  agree.  Owing  to  the  gradual  recovery  of  the  glass 
from  the  effects  of  the  heating  to  which  it  was  subjected  when  the 
thermometer  was  made,  the  zero-point  rises,  at  first  rapidly,  later 
slowly. 

One  of  the  oldest  forms  of  self-registering  thermometers  provided 
with  a  contrivance  to  mark  the  highest  or  lowest  temperature  ob- 
taining in  a  given  interval  of  time,  is  that  of  Six,  made  in  the 
eighteenth  century.  It  consists  of  a  glass  tube  bent  twice  at  right 
angles,  and  furnished  with  a  bulb  at  each  end.  The  bulbs  are  filled 
with  spirit,  except  that  a  bubble  of  air  is  placed  in  the  smaller  one. 
The  bends  of  the  tube  are  occupied  by  a  column  of  mercury.  Two 
steel  pins  sealed  in  glass  tubes  have  hairs  attached  to  them,  so  that 
they  may  retain  any  position  reached  by  being  pushed  by  the  mercury 
column.  A  magnet  is  emplpyed  to  set  these  indexes.  When  the 
temperature  rises,  the  spirit  in  the  large  bulb  expands,  and  pushes 
the  index  and  column  of  mercury  before  it.  When  the  temperature 
falls,  the  spirit  contracts,  and  the  pressure  of  the  air-bubble  in  the 
small  bulb  drives  the  column  of  mercury  back,  which  in  turn  pushes 
the  minimum  index  before  it  as  soon  as  the  temperature  falls  below 
that  at  which  the  instrument  was  set.  The  defects  of  the  instru- 
ment are — it  must  always  be  kept  in  the  vertical  position,  otherwise 


126  PRACTICAL  SAXITARY  SCIEXCE 

the  spirit  may  pass  the  mercuny  at  the  bends  of  the  tube.  The 
mercuiy  tends  to  pass  beyond  the  ends  of  the  indexes  so  that  small 
quantities  are  retained  by  them. 

Modern  maximum  and  minimum  thermometers  are  now  always 
distinct  instruments.  The  student  is  ad\-ised  to  study  these  by 
personal  inspection  at  the  show-rooms  of  a  good  meteorological 
instrument  maker. 

Rutherford's  maximum  thermometer  consists  of  an  ordinary 
mercury  thermometer,  with  an  iron  index  introduced  into  the  bore 
(mercury  does  not  wet  iron).  With  rise  of  temperature  the  index 
is  pushed  before  the  column  of  mercury;  with  fall  of  temperature 
the  mercurN'  at  once  parts  company  with  the  index.  The  liquid  of 
the  minimum  thermometer  is  alcohol,  and  the  index  glass  (alcohol 
wets  glass) .  When  the  temperature  rises,  the  alcohol  flows  past  the 
index  without  mo^'ing  it ;  when  it  falls,  the  index  is  carried  by  the 
retreating  surface  of  the  alcohol  by  capillarity. 

In  estimating  the  weight  of  volumes  of  air  and  aqueous  vapour  at 
\"ar3ang  temperatures  and  pressures,  it  is  necessary  to  understand 
aright  the  meaning  of  '  densit}-,'  '  specific  gravity,'  and  '  relative 
density.'  Density  is  defined  as  the  mass  of  unit  volume  (mass  being 
the  amount  of  matter  as  measured  by  inertia) ;  specific  gravity  is 
the  ratio  of  the  weight  of  a  certain  volume  at  a  given  temperature 
and  pressure  to  the  weight  of  an  equal  volume  of  a  standard  sub- 
stance at  the  same  temperature  and  pressure.  vSince  the  unit 
volume  is  I  c.c,  and  the  unit  mass  i  gramme,  it  follows  that  water  is 
the  standard  substance  whose  density  is  unity.  When  the  density 
of  oxygen  is  spoken  of  as  i6,  it  is  meant  that  the  specific  gravity  of 
oxygen  is  i6,  h\-drogen  being  taken  as  the  standard;  the  real 
densit}'  (mass  of  i  c.c.  0)  is  0-0014  gramme.  It  is  preferable  to  use 
the  phrase  '  relative  density  '  of  oxygen,  etc.,  and  consider  it  as 
meaning  the  same  thing  as  specific  gravity  when  air  or  hydrogen  is 
the  standard.  The  atomic  weights  of  gaseous  elements  such  as  H, 
N,  etc.,  represent  their  relative  densities,  whilst  the  relative  densities 
of  compound  gases  are  represented  by  half  their  molecular  weights. 
The  relative  density  of  0  is  16,  that  of  CO2  22,  H  being  the  standard. 
The  relative  density  of  air  referred  to  the  same  standard  is 
14-47. 
In  hygiene  it  is  customary  in  calculating  the  weights,  etc.,  of  gases 


AIR 


127 


to  take  air  as  the  standard.     The  relative  density  of  H,  is  therefore 

;  of  O, ;  of  COo, :  and  of  water  vapour,  —^  . 

14-47'       ^'14-47  -14-47  ^  14-47 

In  the  metric  system  the  weight  of   a  litre  of  H  at  o^  C  and 
760  millimetres  Hg=  0-0896  gramme. 

In  English  measure  the  weight  of  a  cubic  foot  of  air  at  32°  F.  and 
30  inches  Hg=  566-86  grains. 

The  pressure  of  water  vapour  increases  with  its  temperature  until 
at  boiling-point  it  equals  that  of  the  atmosphere  (30  inches  Hg). 

The  following  figures  are  extracted  from  a  table  of  vapour  tensions : 


32°  F.  =o-i8i  inch  pressure 

33°  F.=o-i88     , 

34°  F.  =0-196     , 

42°  F.  =0-267     . 

43°  F.  =0-277     > 

44°  F.  =0-288     , 

50°  F.  =0-361     , 

52°  F.  =  0-388     , 

53°  F.  =0-403     , 

54°  F.  =0-418     , 

62°  F.-0-556     , 

63°  F.  =  0-576     , 

64°  F.  =0-596     , 

Example. — Find  the  weight  of  a  cubic  foot  of  aqueous  vapour  at 
62°  F. 

At  this  temperature  the  tension  or  pressure  is  0-556  inch.  As 
the  relative  density  of  aqueous  vapour  (air  being  the  standard)  is 

,  or  0-622,  it  is  necessary  to  find  the  weight  of  a  cubic  foot 
14-47  . 

of  dry  air  at  62°  F.  and  0-556  inch  pressure,  and  multiply  the  result 

by  0-622. 

The  weight  of  a  cubic  foot  of  dry  air  under  these  conditions  of 

temperature  and  pressure  will  be  given  by  finding  the  fourth  term  x 

of  the  proportion : 

521  :  491  ::  566-86  grains  :'.i; 
30  :  0-556  -       - 

491     0-556       ^^  „^ 
X  =  "P-  X  ^^^^  X  566  -86  =  9  -9  grams, 
521       30       -i^  V  y  t)         ' 


i-'S  PRACTICAL  SAXITARY  SCIENCE 

and  this  multiplied  by  0-622==  weight  of  aqueous   vapour=  6*i6 
grains. 

The  pressure  of  aquei)us  \'upt)ur  is  constant  for  a  given  tem- 
perature, whether  it  is  in  vacuo  or  mixed  with  a  gas  or  gases,  and 
varies  directly,  as  has  aliead\^  been  stated,  as  the  temperature. 

Two  other  types  of  problem  arise  in  connection  with  this  subject 
— namel3',  (i)  finding  the  weight  of  a  volume  of  air  saturated  with 
vapour  at  a  given  temperature  and  pressure;  and  (2)  finding  the 
weight  of  a  volume  of  air  partially  saturated  with  vapour  at  a 
given  temperature  and  pressure. 

Example  i. — Find  the  weight  of  a  cubic  foot  of  air  saturated  with 
aqueous  vapour  at  62°  F.  and  30  inches  Hg. 

By  the  table  of  vapour  tensions  it  is  seen  that  62°  F.  corresponds 
with  0-556  inch  Hg.  As  the  total  pressure  of  air  and  vapour  is 
30  inches,  the  pressure  exerted  by  the  air  alone  must  be  30-0-556, 
or  29-444  inches.  The  problem,  therefore,  resolves  itself  into 
finding  the  weight  of  a  cubic  foot  of  dry  air  at  62°  F.  and 
29-444  inches,  and  that  of  a  cubic  foot  of  aqueous  vapour  at 
62°  F.  and  0-556  inch. 

491     29-444 

—  X  -^^  X  566-86  =  524-32  grains  (weight  of  dry  air). 

^x    ^- X  566-86  X  0-622=  6-16   grains    (weight   of    aqueous 
vapour) . 

. '.  the  cubic  foot  of  saturated  air 

=  524-32  +6*i6  grains=  530-48  grains. 

Example  2. — Find  the  weight  of  a  cubic  foot  of  air  partially 
saturated  with  aqueous  v^apour  at  62°  F.  and  30  inches,  dew-point 
being  50°  F. 

The  dew-point  is  the  temperature  of  complete  saturation  of  the 
atmosphere.  If  the  atmosphere  be  raised  in  temperature,  its 
capacity  for  holding  aqueous  vapour  will  be  increased;  if  lowered, 
this  capacity  will  be  diminished.  When  the  temperature  is  lowered 
below  the  dew-point,  vapour  is  deposited  in  the  fluid  form. 

Vapour  tensions  in  the  above  table  correspond  with  temperatures 
of  complete  saturation  or  dew-points,  hence,  in  problems  of  the  tyjje 


A IR  129 

under  consideration,  if  the  dew-point  be  not  given,  it  must  be  found- 
This  may  be  done  directly  by  such  instruments  as  Daniell's  or 
Regnault's  hygrometers,  or  indirectly  by  Glaisher's  formula,  or  by 
Apjohn's  formula. 

In  the  indirect  method  the  wet  and  dry  bulb  thermometer  are 
used.  By  Glaisher's  formula  the  dew-point=  D  — G(D  — W)  where 
D  =  temperature  of  dry  bulb,  G  =  Glaisher's  factor  for  reading  of 
dry  bulb,  and  W  =  temperature  of  wet  bulb. 

By  Apjohn's  formula  : 

For  temperatures  above  32°  F. : 


/  d       h\ 
For  temperatures  below  32°  F.: 


^"^     V87'^30. 


\96^30/' 
Where 

P  =  pressure  of  aqueous  vapour  at  dew-point. 
p  =  pressure  of  aqueous  vapour  at  temperature  of  wet  bulb. 
d  =  difference  in  degrees  F.  between  dry  and  wet  bulbs. 
h  =  height  of  barometer  in  inches. 

Returning  to  the  problem,  when  the  dew-point  50°  F.  has  been 
found,  the  pressure  of  the  aqueous  vapour  0-361  inch  is  obtained 
from  the  table  of  vapour  tensions. 

The  problem  is  resolved  as  before  into  two  portions — viz.,  the 
weight  of  dry  air  at  62°  F.  and  pressure  30  -0-361  inches,  and  the 
weight  of  vapour  at  62°  F.  and  pressure  0-361  inch. 

4Q1     20-630       ^^  „^  „        . 

1^  X  -^^  X  566-86=  527-8  grams. 

491     0-361       ^^  „^        ^  -        . 

T^  X  -^^ — -  X  566-86  X  0-622=  3-98  grams. 

527-8  +  3-98=531-78  grains. 

Relative  humidity  represents  the  ratio  between  the  weight  of 
aqueous  vapour  present  in  a  given  volmne  of  air,  and  the  weight 
of  vapour  which  would  be  required  to  saturate  the  same  volume 
of  air  under  similar  conditions  of  temperature  and  pressure,  and 
is  expressed  as  a  percentage. 

9 


130  PRACTICAL  SANITARY  SCIEXCE 

Consider  the  last  example,  in  which  the  temperature  is  62°  F. 
and  the  dew-point  50°  F. : 

Relati\e  humidity  = 
pressure  at  50°  F.  X  —  X  —  x  566-86  x  0-622     pressure  at  50°  F. 

pressure  at  62°  F.  x  ^  x  _^  x  566-86  x  0-622     pressure  at  62°  F. 

0-361  ,  ,         0-361 X 100     ^ 

=  f.;-Ff:',  or  expressed  as  a  percentage,  .^ —  =  64-9  per  cent. 

The  composition  of  the  air  expired  from  the  lungs  contrasted 
with  ordinary  air  demonstrates  the  invariable  nature  of  the  X  and 
the  limits  of  variation  of  O  and  COo. 

Ordinary  Air.  Expired  Air. 

O     -         -        -         -     20-96  per  cent.  16-4  per  cent. 

N     -        -        -        -    79-00       ,,  79-0       ,, 

COo-        -        -        -      0-04       ,,  4-6 

The  practically  uniform  composition  of  the  air  all  over  the  earth 
is  maintained  by  variations  of  temperature  leading  to  variations  of 
voliune  and  pressure,  with  resulting  air-currents,  diffusion  of  gases, 
the  above-named  circulation  affected  by  respiration  of  animals, 
transpiration  of  plants,  rain,  etc. 

Oxygen  is  the  most  important  constituent  of  the  air,  in  that  it  is  a 
prime  necessity  to  life.  Its  quantity  is  diminished  by  respiration, 
putrefaction,  combustions  of  all  types,  and  at  high  altitudes. 

The  estimation  of  O  may  be  readily  carried  out  in  the  following 
ways : 

I.  The  nitric  oxide  (NO)  method. 

This  method,  although  it  has  been  adversely  criticized,  yields, 
in  careful  hands,  excellent  results.  The  reaction  is  represented  b3^ 
the  equation: 

2XO  +  O0-2NO2. 

The  NOg  is  soluble  in  water.  There  is  a  contraction  of  three 
volumes  of  the  mixture  for  every  one  volume  of  0,  therefore  one- 
third  of  the  contraction  represents  the  0. 

To  a  sample  of  air  in  a  gas  burette  excess  of  nitric  oxide  prepared 
from  Cu  turnings  and  HN0.j  is  added.     The  mixture  is  passed  into 


AIR 


131 


an  absorption  pipette  charged  with  water.  The  ruddy  fumes  of 
NO2  are  rapidly  absorbed,  and  after  passing  the  gas  backwards  and 
forwards  a  few  times  the  reading  becomes  constant.  One-third  of 
the  contraction  represents  the  O. 


Fig.  25. — Hempel's  Gas  Burette  and  Absorption  Pipette. 

2.  Hempel's  gas  burette  and  absorption  pipette. 

In  the  figure  the  mounted  tube— the  gas  measurer— next  to  the 
bulbs  is  graduated  into  c.c's.  and  tenths;  the  other— the  levelling- 
tube — is  plain. 

The  absorption  pipette  used  is  a  double  one,  consisting  of  four 


132  PRACTICAL  SAXITARY  SCIEXCE 

bulbs;  the  first  and  largest  contains  alkali  and  pyrogallic  acid  (dis- 
solve i6o  grammes  KOH  in  130  c.c.  water,  producing  about  200  c.c. 
of  solution ;  in  this  dissoh'e  10  grammes  pyrogallic  acid:  if  these  pro- 
portions are  not  adhered  to,  evolution  of  CO  may  take  place  during 
absorption  of  O.  and  cause  error) ;  the  second  and  fourth  are  empty; 
whilst  the  third  contains  water  to  seal  off  the  atmosphere.  The 
reagent  absorbs  O  and  COo-  The  graduated  burette  is  supplied  at 
the  upper  end  with  a  stopcock  and  a  sliort  piece  of  fine  pressure 
tubing  (carrying  a  screw  clip)  which  connects  it  with  the  small 
manometer  U-tube  of  the  bulbs.  In  order  that  this  piece  of  tubing 
may  be  as  short  as  possible,  the  bulbs  are  raised  on  a  block,  so  that 
the  end  of  the  manometer-tube  is  near  to  the  burette.  The  burette 
and  the  levelling-tube  containing  water  are  connected  at  their  lower 
ends  b}'  rubber  tubing. 

In  making  an  estimation,  first  mark  on  the  ivory  slip  the  height 
at  which  the  coloured  liquid  stands  in  the  capillary  U-tube,  turn  the 
stopcock  so  that  connection  is  made  between  the  burette  and  bulbs, 
then  raise  the  levelling-tube  until  all  the  air  is  driven  over  out  of 
the  burette  into  the  bulbs.  Now  connect  the  atmosphere  with 
the  burette,  and  lower  the  levelling-tube  until  a  definite  quantity 
of  the  particular  atmospliere  (say  25  or  50  c.c.)  is  admitted.  Then 
make  connection  with  the  bulbs,  and  raise  the  levelling-tube  until 
this  quantity  of  air  is  dri\-en  o\er  into  the  absorption  apparatus. 
Turn  the  stopcock  off,  screw  down  the  clip,  and  unfasten  the  bulbs 
from  the  burette.  Shake  carefully  for  ten  or  fifteen  minutes,  re- 
unite with  burette,  and  bring  back  the  air  by  lowering  the  levelling- 
tube.  Repeat  these  manipulations  until  a  constant  volume  is 
obtained,  when  the  liquid  stands  at  the  original  mark  in  the  U-tube 
and  the  burette  is  levelled.  The  decrease  in  volume  is  due  to  the 
O  and  COo  absorbed.  Deduct  the  CO2  obtained  by  Pettenkofer's 
method,  and  the  remainder  represents  the  O.  This  volume  of  O 
is  then  reduced  to  standard  temperature  and  pressure. 

Since  the  temperature  should  not  vary  during  the  operation,  the 
burette  must  not  be  handled.  The  absorption  reagent  in  the  first 
bulb,  the  water  in  the  third,  and  the  water  in  the  burette,  should 
all  be  saturated  with  air  before  commencing  the  estimation.  It  is 
to  be  noted  that  the  pyrogallic  solution  will  absorb  besides  0  other 
gases,  such  as  H._,S,  SOo,  HCl,  etc. 


AIR  133 

3.  Where  accurate  estimations  are  required,  tlie  combustion 
method  of  Dumas  may  be  used. 

A  measured  volume  of  air  is  drawn  through  KOH  to  free  it  from 
CO2,  and  thence  over  ignited  spongy  copper  in  a  combustion-tube. 
The  copper  fixes  the  O,  and  the  amount  of  the  Jatter  is  estimated 
from  the  difference  in  weight  of  the  copper  and  copper  oxide. 

Carbon  Dioxide.^ — Carbon  dioxide  may  vary  in  an  atmosphere 
from  0-2  to  07  or  o-8  per  cent.  The  quantity  ordinarily  found  in 
a  pure  atmosphere  ranges  from  0-035  to  0-04  per  cent. 

The  atmosphere  of  London  during  a  fog  often  contains  o-o8  per 
cent.  In  a  living-room  lighted  by  coal-gas  the  COg  may  reach 
0-2  per  cent.,  with  an  appreciable  amount  of  CO. 

Carbon  dioxide  arises  from  (i)  animal  respiration;  (2)  combus- 
tion of  all  kinds  of  fuel;  (3)  organic  combustion  in  the  form  of 
putrefaction,  fermentation,  etc.  Its  special  significance  lies  in  the 
fact  that  as  a  product  of  respiration,  it  can  be  made  a  fairly  accurate 
measure  of  the  organic  impurities  which  accompany  it. 

Carbon  dioxide  per  se,  in  the  quantities  commonly  found,  may 
be  considered  harmless.  It  is  generally  agreed  that  the  amount 
furnished  by  respiration  may  not  exceed  0-02  per  cent.  Taking 
0-04  per  cent,  as  the  average  quantity  found  in  the  air,  o-o6  per  cent. 
(o-02  -f  0-04)  will  represent  the  limit  of  CO2  allowable  in  any  atmo- 
sphere contaminated  by  respiration. 

The  number  of  cubic  feet  of  fresh  air  required  to  dilute  the  CO2 
of  a  room,  so  that  this  limit  may  be  preserved,  will  be  found  b}^  the 
formula : 

cubic  feet  CO2  added  x  100 

0-02 

The  quantity  of  COo  added  to  the  air  through  respiration  is, 
roughly,  o-6  cubic  foot  per  head  per  hour.  Substituting  this  figure 
in  the  formula,  it  is  found  that  3,000  cubic  feet  fresh  air  per  head 
per  hour  must  be  admitted  to  living-rooms  if  the  CO2  is  to  be  kept 
within  the  limits  named. 

The  Estimation  of  CO.^  in  the  Atmosphere- — Pettenkofer's  Method. — 
When  CO2  is  shaken  up  with  barj/ta  water  (Ba(0H)2),  insoluble 
BaCOg  is  formed,  and  the  alkahnity  of  the  fluid  is  lessened. 

Take  a  5-litre  air-jar,  cleansed  and  filled  with  water,  into  the 


r34  PRACTICAL  SAX  IT  A  RY  SCIENCE 

apartnit-nt  in  wiiich  tlie  estimation  is  to  be  made.     Pour  out  the 
water  so  that  the  air  may  enter  the  jar,  and  stopper  carefully. 

Prepare  baryta  water  by  adding  about  5  grammes  Ba(0H)2  to 
a  htre  of  distilled  water,  and  accurately  estimate,  in  terms  of 
standard  oxalic  acid  solution,  the  alkalinity  of  25  c.c,  using  phenol- 
phthalein  as  indicator.  The  acid  is  prepared  by  dissolving  2-82 
grammes  of  the  crystals  in  a  litre.  This  solution  is  of  such  strength 
that  I  c.c.  is  equivalent  to  0-5  c.c.  CO.,  at  standard  temperature 
and  pressure. 

Now  add  50  c.c.  of  the  clear  barium  hydrate  solution  to  the 
contents  of  the  jar,  and  roll  it  round  the  interior  for  some  time. 
When,  in  say  twenty  minutes,  the  whole  of  the  COo  is  absorbed 
and  neutralized,  take  out  25  c.c.  of  the  solution  with  a  pipette  and 
rapidly  titrate  it  with  the  standard  oxalic  acid,  delivered  from  a 
burette.  The  difference  in  alkalinity  of  this  and  the  original  25  c.c. 
multiplied  by  2  is  equivalent  to  the  CO2  in  the  jar  in  c.c.  at  N.T.P. 

Reduce  the  volume  of  air  in  the  jar  to  X.T.P.,  and  calculate  the 
percentage  of  CO.2  on  this. 

The  following  is  an  example:  Temperature  15-  C,  pressure 
750  millimetres.  Twenty-five  c.c.  of  the  freshly  prepared  Ba(0H).3 
were  measured  by  pipette  into  a  porcelain  basin,  a  few  drops  of 
phenolphthalein  added,  and  standard  oxalic  acid  run  in  until  the 
pink  colour  just  disappeared  after  thorough  stirring;  21-5  c.c.  of 
the  standard  acid  were  used. 

Fiftv  c.c.  Ba(0H)2  were  run  into  the  jar,  and  after  complete 
absorption  of  the  COo  had  taken  place,  25  c.c.  were  removed  and 
titrated  with  acid :  19-9  c.c.  standard  acid  were  used.  21-5  — 19*9  = 
1-6  c.c;  and  i-6  c.c.  x  2=  3-2  c.c.  =  the  total  amount  of  acid  equiva- 
lent to  the  CO.,  in  the  jar.  But  each  c.c.  of  acid=o-5  c.c.  CO2; 
therefore  3-2  x  0-5=  i-6  c.c,  the  volume  of  CO2  in  the  jar,  or  i-6  c.c 
in  4,950  c.c.  (5,000  c.c.  -50  the  volume  displaced  by  the  Ba(0H)2). 
The  volume  of  this  4,950  c.c.  at  0°  C.  and  760°  millimetres  = 

4950  X  750 


760  X  {i  +(0-0036  X  15)} 

(in  the  C.  scale  ^|.y  or  0-0036=  coefficient  of  expansion  of  gases  per 
degree)  =  4,635  c.c. 

1-6  c.c.  COo  in  4.635  c.c.  air=  0-03  per  cent. 


AIR 


135 


Baryta  water  is  best  prepared  fresh,  but  if  it  must  be  kept,  it 
should  be  stored  in  a  vessel  shut  off  from  the  atmosphere  by  a 
hollow  tube  filled  with  pumice  moistened  with  KOH.  Ba(0H)2  has 
a  slight  action  on  glass,  but  any  error  that  might  arise  through 
liberated  alkalies  is  so  infinitesimal  that  it  may  be  neglected, 
especially  when  a  jar  has  been  used  a  few  times. 

Angus  Smith's  '  household  test  '  consists  in  running  ^-  ounce  of 
clear  lime  water  into  a  10 1-  ounce  bottle.  No  turbidity  will  be 
found  so  long  as  the  CO2  in  the  air  does  not  exceed  the  limit 
allowed- — viz.,  o-o6  per  cent. 

Lunge  and  Zeckendorf's  Method.- — A  bottle  of  70  c.c.  capacity 
and  an  india-rubber  pump  of  the  same  capacity  are  connected  so 
that  air  can  be  pumped  into  the  bottle.  A  weak  standard  solution 
of  NaOH  is  prepared  and  tinted  with  phenolphthalein,  by  adding 
2  c.c.  ^Q  NaOH  containing  i  per  mille  phenolphthalein,  to  100  c.c. 
ammonia-free  distilled  water.  The  ball  of  the  pump  is  squeezed 
until  the  bottle  is  filled  with  the  air  to  be  tested.  Ten  c.c.  of  the 
5^0  NaOH  are  now  placed  in  the  bottle,  and  the  stopper,  through 
which  the  delivery  tube  of  the  pump  and  an  exit  tube  pass,  inserted. 
The  ball  is  then  gently  pressed,  causing  air  to  bubble  through  the 
liquid,  and  the  bottle  is  carefully  shaken  after  each  addition  of  air 
until  the  colour  is  discharged. 

The  number  of  times  the  ball  is  emptied  indicates  the  amount 
of  CO2,  according  to  the  following  table,  compiled  by  Lunge  from 
estimations  made  by  Pettenkofer's  method: 


2 
3 
4 
5 
6 

7 
8 

9 
10 

II 

12 

13 

14 

15 


Per  Cent. 

0-3 

16 

0-25 

17 

0-21 

18 

o-i8 

19 

0-155 

20 

0-135 

22 

0-II5 

24 

o-io 

26 

0-09 

28 

0-087 

30 

0-083 

35 

o-o8 

40 

0-077 

48 

0-074 

Per  Cent. 
0-071 
0.069 
0-066 
0-064 
0-062 
0-058 
0-054 
0-051 
0-049 
0-048 
0-042 
0-038 
0-030 


136  PRACTICAL  SANITARY  SCIENCE 

When,  from  respiration,  CO.,  rises  above  o"o6  per  cent.,  a  certain 
unpleasant  odour  is  experienced  in  rooms,  due  to  the  accompanying 
organic  exhalations,  and  when  much  above  this  figure  headache 
and  even  faintness  may  super^•ene.  Volatile  fatty  acids  exhaled 
from  the  skin  and  H^S  are  responsible  for  most  of  these  unpleasant 
odours. 

A  cubic  foot  of  coal-gas  yields  on  combustion  o-6  cubic  feet  COg. 
It  is  obvious  that  when  COo  is  due  solely  to  the  combustion  of 
coal-gas  the  quantity  ma}'  be  allowed  to  exceed  considerably  the 
above-named  limit. 

Carbon  Monoxide. — This  odourless  gas  possesses  a  special  affinity 
for  haemoglobin,  displaces  oxygen  from  it,  and  thus  destroys  the 
ox\'gen-carrying  function  of  the  blood  and  ultimately  life,  by  cutting 
short  internal  respiration.  When  haemoglobin  is  saturated  to  the 
extent  of  30  per  cent.,  symptoms  of  poisoning  set  in,  and  70  per  cent, 
saturation  is  fatal.  Coal-gas  contains  by  volume  about  6  per  cent. 
CO,  and  when  imperfectly  burnt  leaves  small  quantities  in  the  flue ; 
but  greater  danger  attaches  to  the  escape  of  the  gas  from  ill-con- 
structed taps  and  joints.  The  use  of  coke,  especially  in  cast-iron 
stoves,  is  a  fruitful  source  of  CO.  As  CO^  passes  over  hot  coke  it  is 
reduced  according  to  the  equation  C  -i-C02=  2CO. 

The  carbon  of  the  hot  cast-iron  acts  in  the  same  manner,  reducing 
COo  to  CO.  Solid  particles  of  organic  matter  floating  in  the  atmo- 
sphere become  charred  on  the  exterior  of  the  stove,  and  this  partial 
oxidation  results  in  the  formation  of  CO.  This  gas  is  present  in 
tobacco  smoke. 

The  characteristic  cherry-red  colour  of  CO-hfemoglobin  serves  as 
an  excellent  test  for  the  presence  of  carbon  monoxide.  If  a  few 
drops  of  fresh  mammalian  blood  be  diluted  with  water  down  to 
about  2  per  cent.,  and  the  solution  shaken  up  with  CO,  the  distinc- 
tive colour  is  at  once  formed.  If  dilution  be  extended  to  0-2  per 
cent.,  and  HbCO  fomied  by  shaking  with  the  gas,  the  characteristic 
spectrum  consisting  of  two  bands  between  D  and  E  occupying  nearly 
the  same  position  as  those  of  HbOa,  but  differing  in  that  they  do  not 
disappear  on  the  addition  of  reducing  agents  such  as  (NH^loS  or 
H.,S,  may  be  readily  seen. 

HbCO  may  also  be  distinguished  from  HbOj  by  adding  to  10  c.c. 
of  the  blood  solution  10  to  15  c.c.  20  per  cent,  solution  K4Fe(CN)g 


AIR  137 

and  2  c.c.  acetic  acid  (i  volume  acetic  acid +  2  volumes  H^O).     A 
reddish-brown  =  HbCO ;  greyish-brown  precipitate  =  HbOg. 

The  estimation  of  CO  in  the  air  may  be  performed  by  (i)  Haldane's 
haemoglobin  percentage  saturation  method,  or  (2)  by  the  cuprous 
chloride  method  for  large  quantities. 

I.  The  following  is  Haldane's  account  of  his  method: 
'  A  solution  of  about  i  of  normal  blood  to  100  of  water  is  made; 
also  a  solution  of  carmine  dissolved  with  the  help  of  a  little  ammonia, 
and  diluted  till  its  depth  of  tint  is  about  the  same  as  that  of  the 
blood  solution.  Two  test-tubes  of  equal  diameter  (about  i  inch) 
are  then  selected.  Into  one  of  these  5  c.c.  of  the  blood  solution  are 
measured  with  a  pipette;  into  the  other  about  an  equal  quantity 
is  poured.  Ordinary  lighting  gas  is  then  allowed  to  blow  into  the 
second  test-tube  through  a  piece  of  rubber  tubing  for  a  few  seconds. 
The  test-tube  is  then  quickly  closed  with  the  thumb  before  the  gas 
has  time  to  escape,  and  the  blood  solution  thoroughly  shaken  up 
with  the  gas  for  a  few  seconds.  The  haemoglobin  is  thus  completely 
saturated  with  carbonic  oxide,  and  the  solution  has  now  the  char- 
acteristic pink  tint.  The  carmine  solution,  which  has  a  still  pinker 
tint,  is  now  added  from  a  burette  to  the  5  c.c.  of  normal  blood 
solution  in  the  other  test-tube  until  the  tints  are  the  same  in  the 
two  test-tubes.  Not  only,  however,  must  the  tints  be  equal  in 
quality,  but  they  must  also  be  sensibly  equal  in  depth.  If  the 
carmine  solution  is  too  strong  or  too  weak,  the  latter  will  not  be 
the  case,  and  the  solution  must  be  diluted  or  made  stronger  accord- 
ingly. It  is  usually  easiest  to  make  the  carmine  a  little  too  strong  at 
first,  so  that  on  adding  both  cannine  solution  and  water  equality 
can  be  established.  From  the  amount  of  water  which  is  required 
to  be  added  it  is  easy  to  calculate  the  extent  to  which  the  original 
carmine  solution  needs  to  be  diluted.  The  solutions  are  now  ready 
for  use,  and  the  actual  analysis  is  made  as  follows:  5  c.c.  of  the 
solution  of  normal  blood  are  measured  into  one  of  the  test-tubes, 
and  a  drop  of  the  suspected  blood  placed  in  the  other  test-tube  and 
cautiously  diluted  with  water  till  its  depth  of  tint  is  about  equal 
to  that  of  the  normal  solution.  If  carbonic  oxide  be  present  in 
the  haemoglobin,  a  difference  in  quality  of  the  tints  of  the  two  solu- 
tions will  now  be  clearly  perceptible.  Carmine  solution  is  then 
added  from  the  burette  to  the  nonnal  blood,  and  water  (if  neces- 


13S  PRACTICAL   SAXITARY  SCIEXCE 

san')  to  the  abiiDrinal  bluod,  till  the  tints  arc  equal  in  both  quality 
and  depth.  The  carmine  is  added  by  about  0-2  c.c.  at  a  time,  the 
points  being  noted  at  which  there  is  just  too  httle  and  just  too  much 
carmine,  and  the  mean  being  taken.  The  solution  of  normal  blood 
is  then  saturated  with  coal-gas,  and  the  addition  of  carmine  to  the 
other  test-tube  continued  until  equality  is  again  established  and 
the  amount  of  carmine  noted.  The  percentage  saturation  with 
carbonic  oxide  of  the  abnormal  blood  can  now  be  easily  calculated, 
since  we  know  how  much  cannine  solution  its  saturation  represented 
as  compared  with  what  complete  saturation  represented. 

'  The  method  of  calculation  is  illustrated  by  the  following  ex- 
ample: To  5  c.c.  of  normal  blood  solution  2-2  c.c.  of  carmine  is 
required  to  be  added  to  produce  the  tint  of  the  blood  under  examina- 
tion, and  6-2  c.c.  to  produce  the  tint  of  the  same  blood  fully  satu- 
rated. In  the  former  case  the  carmine  was  in  the  proportion  of 
2-2  in  7-2,  andin  the  latter  of  6-2  in  11-2.  The  percentage  saturation 
(.v)  of  the  haemoglobin  with  carbonic  oxide  is  thus  given  by  the 
following  proportion  sum : 

6-2       2-2 

:  —  : :  100  :  x. 

1 1 -2    y-2 

X  is  therefore  =  55-2.  As  the  compound  of  carbonic  oxide  and 
haemoglobin  is,  to  a  slight  extent,  dissociated  when  the  blood  is 
diluted  with  water,  the  value  found  is  a  little  too  low.  The  cor- 
rections needed  are  as  follows:  Add  0-5  if  30  per  cent,  saturation 
be  found,  i-i  if  50  per  cent.,  i-6  if  60  per  cent.,  2-6  if  70  per  cent., 
4-4  if  80  per  cent.,  lo-o  if  go  per  cent.  Thus,  in  the  above  example 
we  must  add  1-3,  so  that  the  true  saturation  is  56-5  per  cent.  In 
comparing  the  tints,  the  test-tubes  should  be  held  up  against  the 
light  from  a  window,  but  bright  light  should  be  avoided  as  much 
as  possible,  as  it  increases  the  dissociation.  Failing  daylight,  an 
incandescent  burner,  with  a  chimney  of  blue  glass  and  an  opal 
globe,  may  be  used  as  the  source  of  light. 

'  Haemoglobin  brought  into  intimate  contact  with  air  containing 
0-07  per  cent,  of  CO  will  finally  reach  a  state  of  equilibrium  in  which 
it  is  saturated  to  an  equal  extent  with  CO  and  oxygen.  If  the 
percentage  of  CO  or  oxygen  in  the  air  be  increased  or  diminished, 
there  will  be  an  exactly  corresponding  increase  or  diminution  of 


AIR  139 

the  relative  share  of  the  hiemoglobin  which  cither  gas  detains.  Air 
containing  2  x  0-07=  0-14  per  cent,  of  CO  will,  for  instance,  produce 
two-thirds  saturation  with  CO,  and  one-third  saturation  with 
oxygen,  and  so  on.  In  the  living  body  the  proportion  of  CO  taken 
by  the  hgemoglobin  from  respired  air  containing  a  given  percentage 
of  CO  is  not  so  large  as  outside  the  body,  about  i  per  cent,  of  CO 
in  the  air  breathed  being  necessary  to  produce  half  saturation  of 
the  haemoglobin.  The  general  law  of  absorption  is,  however,  much 
the  same,  and  it  follows  that  there  is  a  certain  maximum  of  satura- 
tion for  each  percentage.  With  less  than  0-05  per  cent,  of  CO  in  the 
air  this  maximum  does  not  exceed  33  per  cent,  saturation,  and  the 
corresponding  symptoms  are  scarcely  appreciable,  except  on  mus- 
cular exertion.  With  more  than  about  0-2  per  cent,  the  maximum 
exceeds  60  per  cent,  saturation. 

'  The  detection  and  determination  of  small  percentages  of  CO 
in  the  air  was  formerly  a  matter  of  great,  and  often  almost  insuper- 
able, difficulty.  I  have  recently,  however,  introduced  a  simple 
and,  I  think,  very  satisfactory  method,  depending  on  the  already 
described  action  of  CO  on  blood  solution  in  presence  of  air.  The 
sample  of  air  is  collected  in  a  clean  and  dry  bottle  of  about  4  ounces 
capacity.  The  cork  of  the  bottle  is  removed  in  the  laboratory 
under  a  0-5  per  cent,  solution  of  blood,  and  about  5  c.c.  of  the  air 
allowed  to  bubble  out,  a  corresponding  volume  of  the  blood  solution 
entering.  The  cork  is  then  replaced,  covered  with  a  cloth  to  keep 
off  the  light,  and  shaken  continuously  for  about  ten  minutes,  when 
the  haemoglobin  will  have  reached  the  point  of  saturation  corre- 
sponding to  the  percentage  of  CO  present.  The  solution  is  then 
poured  out  into  a  test-tube,  and  the  saturation  is  determined  with 
carmine  solution  in  the  manner  described  above.  It  is  evident 
that  as  in  each  case  the  saturation  found  corresponds  to  a  definite 
percentage  of  CO  in  the  air,  it  is  easy  to  calculate  this  percentage. 
If  p  be  the  percentage  required,  and  s  the  percentage  saturation 
found,  p  is  calculated  from  the  following  formula: 

5x0-055 
100  — s  " 

Thus,  if  s=  60,  p  is  0-0825.  This  method  may  also  be  used  for  the 
direct  determination  of  carbonic  oxide  in  lighting-gas.     The  latter 


140  PRACTICAL  SAXITARY  SCIENCE 

must,  liowever,  be  lirst  diluted  to  ^}j^,  (or  with  carburetted  water- 
gas  to  jI^)  with  air.  As  it  is  quite  easy  to  make  this  dilution  with 
perfect  accuracy,  the  method  is  an  exact  one,  and  is  not  only  rapid, 
but  a\-oids  the  difficulties  and  sources  of  error  connected  with  the 
ordinary  method  of  determination  by  cu})rous  chloride,  or  by  ex- 
plosion.' 

2.  The  cuprous  chloride  method. 

Cuprous  chloride  is  prepared  from  copper  turnings,  copper  oxide, 
and  strong  HCl.  and  dissolved  in  distilled  water.  This  solution 
absorbs  CO. 

The  air  to  be  treated  is  lirst  freed  from  0  and  COg  by  passage 
through  Hempel's  burette.  The  residue  is  slowly  and  repeatedly 
passed  into  a  second  absorption  pipette  containing  cuprous  chloride 
in  solution.  The  bulb  containing  the  copper  salt  should  be  large, 
the  time  for  absorption  long,  and  the  transference  from  burette  to 
pipette  and  vice  versa  as  often  repeated  as  necessary  to  procure  a 
constant  reading.  The  loss  in  volume,  assuming  that  ethylene, 
acetylene,  etc.,  are  absent,  represents  the  CO  present.  This  method 
is  by  no  means  reliable. 

Ammonia  is  found  in  traces  in  all  atmospheres.  It  is  a  product 
of  putrefaction,  and  although  in  small  quantities  it  seems  to  be 
harmless,  it  should  be  regarded  with  suspicion,  b}-  reason  of  the 
noxious  bodies  which  accompany  it.  It  is  found  in  larger  quantity 
in  air  in  immediate  contact  with  peat.  It  may  be  collected  and 
estimated  by  aspirating  a  know^n  volume  of  air  through  ammonia- 
free  distilled  water,  and  aftenvards  distilling  and  Xesslerising. 

Sulphur  Dioxide,  Ammonium  Sulphide,  and  Sulphuretted 
Hydrogen  are  all  present  in  the  atmospheres  of  cities,  and  are 
hurtful  to  health  and  vegetation.  Sulphur  dioxide  abounds  w^here 
impure  coals  are  consumed,  and  HgS  where  organic  decomposition 
takes  place.  It  is  stated  that  0*06  per  cent.  H2S  in  an  atmosphere 
is  dangerous  to  life,  and  fatal  accidents  in  scw^ers  have  been 
attributed  to  this  gas. 

SO2  may  be  estimated  by  aspirating  a  large  and  known  volume 
of  air  through  bromine  water,  and  precipitating  the  H2SO4  thus 
formed  with  BaCU-  From  the  weight  of  the  insoluble  BaS04  ob- 
tained the  weight  of  SO.,  is  calculated. 

Sulphuretted  Hydrogen  may  be  detected  by  exposing  to  the  air 


AIR  141 

strips  of  filter-paper  moistened  with  lead  acetate,  and  estimated 
quantitatively  by  aspirating  a  known  volume  of  air  through  a 
solution  of  decinormal  iodine  containing  a  little  starch  paste.  Im- 
mediately the  blue  colour  departs  the  aspiration  is  stopped. 

17  milligrammes  HgS  correspond  with  i  c.c.  ^ij  ^^ 
H2S  +  l2=2HI+S. 

Ammonium  Sulphide. — The  violet  colour  produced  by  the  inter- 
action of  (NH4)2S  and  sodium  nitro-prusside  may  be  utihzed  for 
matching  a  standard  solution  with  another  containing  an  unknown 
quantity  of  (NH4)2S. 

Chlorine  may  be  absorbed  in  10  per  cent.  KI  solution,  and  the 
liberated  I  estimated  with  y^  sodium  thiosulphate.  Bromine  may 
be  estimated  in  the  same  way: 

2C1+2KI=2KC1+I2. 

3-5  parts  by  weight  Cl=  i2-6  parts  I,  or  7-9  parts  bromine. 

Nitrous,  Nitric,  and  Hydrochloric  Acids  may  be  estimated  by 
absorption  of  measured  quantities  of  air  in  water,  and  employing  the 
methods  described  in  water  analysis. 

Carbon  Bisulphide. — The  vapour  of  CS2  found  in  the  air  of  india- 
rubber  works  is  estimated  by  passing  it  into  strong  alcoholic  potash. 
This  solution  is  then  acidified  with  acetic  acid,  and  finally  neutralized 
with  CaCOg.  It  is  now  diluted  to  twice  its  volume  with  water  and 
titrated  with  standard  iodine  solution  (i-66  milligrammes  I  per  litre) 
and  starch  paste.  One  c.c.  1=  i  milligramme  CSo-  The  reaction  is 
complete  when  a  faint  blue  tint  appears. 

Chlorine  and  bromine  are  injurious  to  human  beings  in  dilution 
of  o-i  part  per  100,000,  and  the  following  as  noted: 

Iodine  _         _         _         _  _       0-5  part  per  100,000. 

SOaandHCl        -        -        -  -       i-o     „ 

H2S  and  NHg       _         _         _  .  lo-o  parts  per  100,000. 

CO        -----  -  20-0      ,, 

Ozone. — Ozone,  an  allotropic  modification  of  oxygen,  O3,  is  a  gas 
possessing  an  odour  of  phosphorus  and  an  irritating  action  on  the 
cells  of  the  respiratory  and  conjunctival  mucous  membranes.  It  is 
produced  by  electric  discharges  over  the  sea,  and  to  a  greater  extent 
at  night  than  in  the  day.     It  is  stated  that  more  ozone  is  found  in 


142  PRACTICAL  SAXITARY   SCIEXCE 

tlie  winter  (especially  after  snowstorms)  tluiii  in  tlie  smnnier.     It  is 
absent  from  the  air  of  towns,  li\'ing-rooms,  and  foggy  atmospheres. 

Detection  and  Esti^nation  of  Ozone. — Pieces  of  blotting-paper  are 
soaked  in  a  solution  of  KI  and  starch,  and  dried.  These  are  then 
suspended  in  a  cage,  which  protects  them  from  direct  sunlight,  dust, 
and  rain  for  twelve  or  twenty-four  hours;  where  ozone  is  present,  it 
hberates  I,  which  forms  a  blue  colour  with  the  starch.  O3-I-2KI 
+  H2O  =  2KOH  +  I0+O0.  It  should  be  remembered  that  N2O.5, 
HoOo,  and  CI  act  in  the  same  way;  that  free  iodine  may  be  partially 
volatilized,  or  in  part  form  iodide  or  iodate  of  potassium,  instead  of 
blue  iodide  of  starch;  and  that  constant  results  cannot  be  expected 
owing  to  the  variability  in  the  conditions  of  temperature,  light,  and 
moisture. 

Houzeau's  test  consists  in  moistening  faintty  red  litmus-papers 
with  a  solution  of  KI  and  exposing  them  to  the  air.  If  ozone  be 
present  I  is  liberated,  and  alkaline  KOH  is  formed,  which  renders 
the  paper  blue.  Ammonia  and  hydrogen  peroxide  are  the  only 
other  two  gases  which  could  produce  this  result.  As  H2O2  is 
practically  never  present,  NH3  is  the  only  other  gas  to  be  con- 
sidered. If,  therefore,  a  second  piece  of  litmus-paper  untreated  by 
KI  is  exposed  at  the  same  time,  and  if  the  entire  colour  is  not  due 
to  XH3,  the  difference  in  the  shades  of  the  two  papers  must  be 
furnished  by  ozone. 

The  intensity  of  colour  created  by  ozone  acting  on  papers  exposed 
to  the  atmosphere  may  be  matched  by  one  of  a  series  of  ten  papers 
forming  a  standard  scale.  Each  pair  of  papers  is  exposed  to  a 
known  quantity  of  ozone.  Measured  quantities  of  air  are  aspirated 
over  the  papers  in  tubes.  If  the  papers  are  suspended  in  the  atmo- 
sphere, wind  currents,  etc.,  by  bringing  unequal  quantities  of  air 
into  contact  with  them,  will  vitiate  the  results. 

Hydrogen  Peroxide.^ — Aspirate  20  to  100  litres  of  air  containing 
HoO,  through  100  c.c.  distilled  water.  To  10  c.c.  of  the  water  add 
I  drop  of  a  I  per  cent,  potassium  chromate  solution,  2  or  3  drops 
of  25  per  cent.  H2SO4,  and  2  c.c.  of  ether.  Shake  gently  for  some 
time ;  perchromic  acid  is  formed  and  goes  into  solution  in  the  ether, 
rendering  it  blue. 

Phosphoretted  Hydrogen. — When  grades  of  ferro-silicon  rich 
in  silicon  (40  to  Go  per  cent.)  are  exposed  to  water  or  damp  air,  a 


AIR  143 

reaction  takes  place  between  calcium  j)hosi)liide,  Ca.jF^,  an  impurity, 
and  the  water,  resulting  in  the  production  of  PH,;,  and  sometimes 
AsHg. 

The  presence  of  PH3  is  detected  by  aspirating  the  air  containing 
it  over  two  sets  of  filter  papers — (a)  moistened  with  a  solution  of 
AgNOg,  and  {h)  moistened  with  a  solution  of  Pb(C2H302)2-  The 
nitrate  of  silver  only  is  darkened,  no  action  taking  place  between  the 
gas  and  lead  acetate.  As  HgS  darkens  both  papers,  it  is  well  to 
remove  it  before  testing  for  PHg;  this  can  be  readily  accomplished 
by  aspirating  the  air  through  a  solution  of  lead  acetate. 

Suspended  Matter  in  the  Air. — Sol^id  animal,  vegetable,  and 
mineral  particles  float  in  the  atmosphere,  and  tend  to  settle  on 
objects  as  favourablje  conditions  occur.  In  factories  and  work- 
shops the  amount  of  such  matter  may  be  so  great  as  to  be  positively 
dangerous  to  health.  Pathogenic  micro-organisms  adhere  to  dust 
and  are  carried  with  it. 

The  collection  and  microscopical  examination  of  dust  is  effected 
by  aspirating  large  quantities  of  air  over  gelatin,  etc.,  or  through 
water.  In  the  first  case  the  microscope  will  detect  mineral  and 
dead  organic  matter,  and  where  living  bacteria  are  present  these 
will  grow  and  produce  colonies,  which  can  later  be  subcultured  and 
studied  at  length.  In  the  second  a  few  drops  of  the  water  are 
evaporated  on  a  slide  and  the  sediment  microscopically  studied. 

Pouchet's  aeroscope  is  a  simple  instrument  in  which  known 
volumes  of  air  are  aspirated  over  a  drop  of  glycerin  on  a  micro- 
scopic slide;  the  intercepted  particles  are  afterwards  studied 
microscopically. 

The  dust  in  the  atmosphere  of  towns  commonly  exceeds  10  milli- 
grammes per  cubic  metre,  or  from  10,000  to  200,000  particles  per 
c.c.  On  the  top  of  a  lofty  mountain  there  may  be  no  dust,  or  only 
a  few  particles  per  c.c. 

As  to  the  nature  of  the  particles  forming  dust,  it  is  sufficient  to 
say  that  they  are  derived  from  every  conceivable  substance  with 
which  we  have  to  do  that  is  capable  of  existing  in  particulate  form. 
The  most  important  substances,  from  a  health  point  of  view,  are 
solid  particles  capable  of  irritating  the  various  internal  channels 
in  man,  and  bacteria  and  their  spores. 

Sewer  air  contains  less  oxygen  and  more  CO2  than  that  of  the 


144  PRACTfCAL  SAXITARY  SCIENCE 

atmosphere.  Ammonia,  ammonium  sulphide,  and  various  com- 
pound ammonias  emitting  f(ttid  odours,  sulpliuretted  hydrogen, 
and  mairsli-gas,  are  present  in  ever-varying  quantities.  Ground 
air  is  very  rich  in  COg,  especially  in  the  autumn  season  of  the  year. 
Ground  air  should  be  excluded  from  all  living-rooms,  not  only 
because  of  its  own  impurity,  but  because  where  it  is  allowed  entrance, 
other  more  dangerous  gases,  such  as  coal-gas,  sewer-gas,  etc.,  may 
often  enter  too. 

A  sample  of  ground  air  may  be  collected  for  examination  thus: 
A  hollow,  sharp-pointed  steel  cylinder,  with  many  perforations, 
is  pushed  into  the  soil  for  a  distance  of  4  to  6  feet.  The  upper  end 
of  the  cylinder  is  connected  with  an  air-jar,  and  this  in  turn  with 
an  aspirator.  The  jar  being  shut  off  from  the  cylinder,  is  lirst 
emptied  by  the  aspirator ;  connection  is  then  made,  and  the  sample 
collected. 

Besides  COg,  which  may  reach  5  or  6  per  cent.,  small  quantities 
of  XH3,  CH4,  H2S  are  usualty  found. 

Qualitative  Examination  of  Air  for  Noxious  Gases  in  Large 

Amounts. 

Where  the  air  of  factories,  etc.,  contains  noxious  gases,  qualitative 
examination  is  readily  performed  by  aspirating  large  quantities  of 
the  air  through  pure  water  or  other  suitable  solvent.  Where,  how- 
ever, the  gases  are  in  considerable  quantities,  tests  may  be  applied 
direct  to  samples  of  the  air  in  jars.  Occasionally  the  atmosphere 
surrounding  chemical  works,  etc.,  contains  such  large  quantities  of 
CI,  HCl,  SOo,  etc.,  that  this  direct  method  of  examination  may  be 
adopted. 

The  following  gases  may  be  readily  recognised  by  a  few  simple 
chemical  tests : 

HCl,  CO.,,  N2O3.  HNO3,  H^S,  SOo,  CI,  CO,  CS2,  NH3,  (NH4)2S. 

I.  Having  collected  a  sample  in  an  air-jar,  remove  the  stopper 
and  smell  the  gas.  Replace  the  stopper  quickly.  CI  has  a  charac- 
teristic odour.  HCl  has  a  faint  odour  of  chlorine.  SOo  has  a 
characteristic  odour,  so  also  have  NH3,  (NH4)2S,  HgS,  CS,. 

CO2,  CO,  X2O3,  HNO3  have  no  odours. 


AIR  145 

2.  Take  the  reaction  by  moistening  a  red  and  blue  filter-paper 
with  water  and  rapidly  inserting  them  in  the  jar,  fixing  the  ends 
between  the  neck  and  the  stopper.  If  doubt  exist  as  to  the  effect  on 
the  litmus-papers,  the  reaction  may  again  be  taken  when  the  gas  is 
dissolved  in  a  small  quantity  of  distilled  water. 

HCl,  COo,  N2O3,  HNO3,  SOo  are  acid. 

NH3,  (NHJgS  are  alkaline. 

HgS,  CO,  CS2  are  neutral. 

CI  first  reddens  blue  litmus-paper  and  afterwards  bleaches  it. 

3.  Dissolve  the  gas  in  10  c.c.  of  water  by  vigorous  shaking,  and 
if  the  reaction  be  acid,  to  2  or  3  c.c.  of  the  solution  add  a  drop  or 
two  of  AgNOg  solution.     A  white  precipitate  indicates 

[a]  HCl.  Acidity  marked;  precipitate  marked  and  soluble 
in  (NH4)H0;  insoluble  in  HNO3. 

(6)  COg.  Acidity  slight;  precipitate  slight.  Addition  of 
Ba(0H)2  produces  turbidity,  increased  on  further  addi- 
tion of  a  drop  or  two  of  (NHJHO. 

(c)  SOg.     Odour  characteristic;  acidity  marked;  precipitate 

marked,  soluble  in  HNO3.  Two  or  three  c.c.  of  the 
solution  from  the  jar  added  to  iodide  of  starch  will 
decolourize  it.  If  2  or  3  c.c.  of  the  same  solution  be 
heated  with  a  drop  of  HCl,  a  granule  of  Zn,H2S  will  be 
formed,  which  will  darken  lead  acetate  paper. 

[d]  No  precipitate,  HNO3.     Peiform  the  brucine  test;  also  the 

diphenylamine  test. 
{e)  No  precipitate,  NgOg  (now  HNOg).     Test  for  nitrous  acid 
with  KI,  starch,  and  H2SO4;  and  perform  the  meta- 
phenylene-diamine  test. 

4.  If  the  reaction  be  alkaline,  the  gas  is  either 

[a)  NH3.     Odour  characteristic.     To  2  or  3  c.c.  of  the  solution 

from  the  jar  add  a  drop  or  two  of  Nessler's  reagent,  and 
the  well-known  yellow  colour  is  developed.     Or 

[b)  (NH4)2S.     Odour  characteristic.     Nessler's  reagent  causes 

a  t)lack  colour  when  mixed  with  the  solution  from  the 
jar.  To  a  few  c.c.  add  a  drop  or  two  of  sodium  nitro- 
prusside,  and  a  violet  colour  rapidly  appears. 

5.  If  the  reaction  is  neutral,  one  or  other  of  the  following  is 
present : 

{a)  HoS.  Odour  characteristic.  Lead  acetate  paper  is  dark- 
ened. Solutions  of  salts  of  iron,  lead,  and  copper  pro- 
duce the  dark-coloured  sulphides  of  these  metals. 

10 


146  PRACTICAL  SAXITARY  SCIENCE 

[b)  CSo.  A  liquid  at  ordinary  temperatures.  Set  alight  a 
drop  on  a  porcelain  slab,  and  note  the  yellow  deposit  of 
sulphur  left  behind. 

6.  The  only  gas  which  lirst  reddens  blue  litmus-paper  and  then 
slowly  bleaches  it  is  CI. 

Odour  characteristic.  Suspend  a  moist  KI  pa])er  in  the 
jar.  Free  I  will  be  liberated  and  darken  the  paper;  later 
the  darkened  paper  will  be  bleached.  Chlorine  added 
to  a  mixture  of  ferrous  sulphate  and  potassium  sulpho- 
cyanide  produces  a  red  colour. 

Note  the  differences  between  H^S  and  (NH4)2S.  HoS  has  a 
neutral  reaction,  odour  of  rotten  eggs  only,  and  forms  no 
colour  ^\•ith  nitro-prusside  of  sodium.  (XH4)2S  has  an 
alkaline  reaction,  odour  of  rotten  eggs  and  NH3,  and 
produces  a  violet  colour  with  sodium  nitro-prusside. 

7.  CO  is  distinguished  by  absence  of  odour,  no  reaction  \\itli 
litmus,  and  by  the  characteristic  colour  and  spectrum  when  shaken 
with  blood. 

Bacteriolog'y  of  the  Air.^ — The  number  of  micro-organisms  in  the 
air  is  largely  determined  by  the  quantit}'  of  dust  particles  in  it. 
Bacteria  adhere  to  and  are  carried  by  dust  particles;  the  types 
found  in  air  are  for  the  most  part  chromogenic  saprophytes,  yeasts, 
and  spores  of  moulds.  The  number  varies  with  the  altitude,  date, 
and  amount  of  recent  rains,  and  other  factors.  Numerical  detei'- 
mination  is  of  ser\-ice  as  a  means  of  comparing  methods  of  ventila- 
tion. Gordon,  in  his  report  on  the  ventilation  of  the  House  of 
Commons,  1906,  states  that  in  the  dust  of  the  chamber  there  were 
present  per  gramme:  Streptococci,  10  to  1,000;  B.  enteritidis  sporo- 
genes,  1,000  to  10,000;  B.  coli,  1,000  to  10,000;  total  number  of 
bacteria,  100,000  to  1,000,000. 

Haldane  found  the  number  of  bacteria  in  the  air  of  book-binding 
workshops  per  litre  6,  cloth  factories  11,  tailoring  workshops  12, 
ropemaking  premises  327. 

Andrewes  has  shown  in  his  reports  to  the  Local  Govemment 
Board  that  in  certain  circumstances  characteristic  sewage  bacteria 
are  found  in  the  air  of  drains  and  sewers.  He  has  carefully  studied 
the  characters  of  the  organisms  found  in  drain  and  sewer  air:  B.  coli 
oi  drain  air  corresponds  in  characters  with  the  same  organism  as 


AIR  147 

found  in  sewage.  He  considers  that  splashing  produces  droplets 
so  minute  as  to  be  carried  some  distance  in  the  air,  and  that  through 
these  bacteria  are  conveyed.  He  concludes  that  tlie  number  of 
faecal  bacteria  in  drain  air  is  largely  proportional  to  the  faecal  content 
of  the  sewage. 

The  original  methods  of  enumerating  bacteria  in  the  air  designed 
by  Pasteur,  Koch,  and  Hesse  are  not  in  use  to-day.  Modern 
methods  are  of  two  types:  (i)  Those  based  on  filtration;  (2)  those 
based  on  bubbling  air  through  a  suitable  liquid.  It  is  well  to  sow 
both  agar  and  gelatin  plates,  as  in  most  instances  gelatin  liquefies 
in  a  short  time.  Some  form  of  aspirator  is  used,  and  where  the  air 
passes  through  a  liquid,  care  must  be  taken  that  the  air  passes  slowly 
and  regularly,  in  order  that  the  bubbles  may  burst  one  by  one. 

1.  Filtration  Methods. — Petri  used  a  sterile  wide  tube  containing 
alternate  segments  of  wire  gau:^e  and  fine  sand.  When  aspiration 
was  complete,  the  sand  was  mixed  with  sterile  gelatin,  and  plates 
poured.  Frankland  substituted  for  sand  glass-wool  or  asbestos. 
After  aspiration  the  filtering  medium  was  shaken  up  with  broth, 
and  with  this  gelatin  plates  were  sown.  But  these  insoluble  filtering 
media  are  now  displaced  by  soluble  media. 

Sodium  sulphate  is  fused,  powdered,  sifted,  and  introduced  into 
a  glass  tube,  one  end  of  which  is  drawn  out  and  sealed  in  the  flame, 
and  the  other  end  plugged  with  wool.  The  whole  is  sterilized  in 
the  hot-air  sterilizer.  When  about  to  be  used,  the  pointed  end  is 
broken  off,  and  the  other  plugged  and  connected  to  an  aspirator. 
When  aspiration  is  finished  the  powdered  sulphate  is  dissolved  in  a 
measured  volume  of  broth,  and  plates  are  sown  with  known  quan- 
tities of  the  liquid. 

A  mixture  of  glass-wool  and  one-third  its  weight  of  cane-sugar  is 
used  as  a  filtering  medium  in  much  the  same  manner. 

2.  Bubbling  Methods.- — Miguel  used  a  Pasteur  flask  with  two  side 
tubulures — one  drawn  out  and  sealed,  the  other  plugged  with  wool. 
A  small  measured  quantity  of  water  was  placed  in  the  flask,  and  the 
whole  sterilized  in  the  autoclave.  Aspiration  of  air  through  the 
water  was  slowly  effected,  and  when  a  sufficient  quantity  had  passed 
through,  the  sealed  tubulure  was  broken,  and  measured  quantities 
of  the  water  sown  in  media,  and  the  latter  incubated. 

Laveran    uses   two   glass  tubes   connected   at   the   junction   of 


148  PRACTICAL  SAXITARY  SCIExXCE 

their  upper  and  middle  thirds  by  a  bridge  tube.  Each  of  the  up- 
right tubes  is  plugged  with  an  india-rubber  stopper  carrying  a 
pipette  which  reaches  to  the  bottom  of  the  tube.  The  pipettes  are 
plugged  abo\-e  with  wool.  One  pipette  is  graduated  in  tenths  of  a 
c.c.  The  tube  carrjang  the  other  pipette  has  a  10  c.c.  mark  on  the 
glass.  Ten  c.c.  of  a  i  per  cent,  solution  of  sugar  in  water  are  placed 
in  this  tube,  and  the  apparatus  is  autoclaved. 

When  about  to  use,  remove  the  plug  from  the  pipette  which  dips 
in  the  sugar  solution,  and  connect  the  other  pipette  with  an  aspirator. 
The  aspirated  air  bubbles  through  the  solution,  into  the  first  tube, 
through  the  horizontal  connecting-tube,  down  through  the  second 
tube,  and  passes  out  through  the  pipette  connected  \\'ith  the 
aspirator.  When  sufhcient  air  has  bubbled  through,  gently  aspirate 
the  sugar  solution  into  the  entry  pipette  to  wash  it;  then  run  the 
liquid  through  the  connecting-tube  into  the  second  upright  tube,  and 
so  into  the  second  and  graduated  pipette ;  repeat  this  several  times 
so  as  to  collect  all  the  bacteria  that  have  been  caught  on  the  glass. 
Now,  by  the  graduated  pipette,  distribute  the  liquid  into  the  various 
culture  media. 

This  method  is  suitable  for  large  volumes  of  air,  and  supplies 
plenty  of  material  for  sowing  cultures.  It  is  thus  one  of  the  best 
methods  for  detecting  pathogenic  bacteria. 

Suppose  250  litres  have  been  aspirated  and  20  colonies  have 
grown  on  a  gelatin  plate  so\\ti  with  i  c.c.  of  the  sugar  solution: 

20  X  10  X  -^-:~  =Soo  =  nmnber  of  aerobic  organisms  contained  in  a 

cubic  metre  of  air  (1,000  litres  =1  cubic  metre). 

A  simple  method  which  may  be  made  by  careful  manipulation 
fairly  accurate  is  that  of  plate  exposure :  Pour  Petri  plates  of  gelatin 
and  agar.  When  solid,  expose  them  to  the  air  under  examination 
by  removing  their  covers  for  selected  periods — say  fifteen  to  thirtj' 
minutes.  At  the  end  of  the  period  replace  covers  and  incubate. 
When  organisms  have  developed,  count  and  calculate  to  units  of 
area  and  time — say  per  square  foot  per  minute  (area  of  a  Petri  dish  = 
iry^  where  r  is  the  radius).  If  necessar}-,  the  various  subcultural 
methods  may  be  resorted  to  for  the  identification  of  individual 
species. 


CHAPTER  XI 

FOODSTUFFS 

MILK. 

Since  the  milk  of  the  cow  is  used  to  a  much  greater  extent  than 
that  of  any  other  mammal,  its  composition  and  properties  have 
been  much  more  thoroughly  studied.  Its  liabiHty  to  early  decom- 
position and  the  fact  that  it  forms  an  excellent  culture  medium  for 
bacteria  render  it  necessary  that  the  strictest  attention  should  be 
paid  to  its  production,  collection,  and  distribution: 
Composition  of  cow's  milk: 

Per  Cent. 
8775 


Water 

Proteins 

Lactose 

Fat 

Ash 


3-50 
4-60 

3-40 

075 


Our  knowledge  of  the  pr  oteins  of  milk  is  still  very  incomplete 
The  application  of  ordinary  and  crude  chemical  methods  to  the 
investigation  of  vital  products  necessarily  leads  to  unsatisfactory 
results.  The  preparation  of  pure  proteins  is  a  most  difficult  task, 
and  the  probabilities  are  that  in  many  cases  where  it  is  thought 
that  a  pure  product  has  been  isolated  it  is  contaminated  by  re- 
agents. 

The  proteins  of  the  milks  of  different  animals  vary^  considerably. 
On  the  addition  of  an  acid  to  cow's  milk  or  goat's  milk,  a  curd  or 
clot  composed  of  casein  is  formed,  and  it  is  believed  that  in  these 
cases  the  casein  is  chemically  combined  with  the  phosphates  of  the 
alkaline  earths.  In  human  milk  and  the  milk  of  the  ass  and  mare 
no  such  clot  is  produced  on  the  addition  of  acid.  Here  it  is  believed 
that  the  protein  is  not  combined  with  phosphates.  Besides  casein, 
a  second  protein  (lactalbumin)  is  found  in  all  milks.     Storch  de- 

149 


150  PRACTICAL  SAXITARY  SCIEXCE 

scribes  a  miico-protoin  which  he  holds  forms  a  gelatinous  envelope 
round  the  fat  globules.  Amylolytic  and  proteolytic  ferments  are 
said  to  occur  in  milk. 

The  jirotein  molecule  is  highly  complex,  as  e\-idenced  by  its 
indiffusibility.  Through  the  action  of  enzymes  in  the  presence  of 
acids  and  alkalies  these  complex  bodies  are  hydrolysed,  passing 
through  various  intermediate  stages  (varieties  of  albumoses)  into 
diffusible  peptones.     Further  hydrolysis  produces  amino-acids. 

The  number  of  proteins  in  the  milk  of  the  cow  has  been  variously 
stated.  Duclaux  maintains  that  there  is  only  one — casein,  existing 
in  two  forms,  coagulable  casein  and  non-coagulable  casein.  Ham- 
marsten  describes  two- — casein,  corresponding  to  Duclaux's  coagu- 
lable casein,  and  lactalbumin,  corresponding  to  Duclaux's  non- 
coagulable  casein.  This  observer  admits  that  lactalbumin  has  the 
properties  of  a  true  albumin,  and  closely  resembles  serum  albumin; 
but  holds  that,  owing  to  differences  in  certain  physical  constants, 
it  is  a  distinct  body.  Hammarsten's  casein  and  Halliburton's 
caseinogen  are  doubtless  the  same  body.  Sebelein  describes  a 
globulin  in  milk. 

Casein. — \\'hen  pure,  this  is  a  white,  non-crystalline,  odourless, 
and  tasteless  substance,  insoluble  in  water,  weak  acids,  alcohol,  and 
ether.  It  is  soluble  in  stronger  acids  and  weak  alkalies.  It  appears 
to  possess  a  peculiar  affinity  for  calcium  phosphate  as  it  is  almost, 
if  not  quite,  impossible  to  free  it  from  this  salt.  Casein  contains 
less  sulphur  than  either  globulin  or  albumin,  but  much  more  phos- 
phorus. In  solution  in  weak  alkalies  it  is  Isevo-rotatory  on  polarized 
light.  Bechamp  holds  that  it  is  a  weak  dibasic  acid,  forming  two 
types  of  salts,  and  his  view  is  confirmed  by  S51dner.  This  body  is 
readily  prepared  by  diluting  milk  about  five  times  and  adding  acetic 
acid  until  the  solution  contains  o-i  per  cent.  The  precipitate  formed 
carries  down  the  fat  with  it.  This  precipitate  is  well  washed  on  a 
filter,  dried  by  pressure,  and  dissolved  in  the  least  excess  of  am- 
monia. By  this  means  the  fat  rises  to  the  surface  and  the  under- 
lying solution  can  be  siphoned  off.  It  is  again  precipitated  by 
acetic  acid,  washed,  dried,  and  redissolved  in  ammonia.  After 
three  or  four  such  precipitations  the  casein  is  rubbed  up  with 
alcohol  in  a  mortar.  The  alcohol  is  poured  off,  and  the  residue 
treated  in  the  same  manner  with  ether.     It  is  afterwards  extracted 


MILK  151 

with  ether  in  a  Soxhlet  apparatus  to  remove  the  fat.  The  treat- 
ment with  alcohol  and  ether  is  repeated  a  number  of  times.  It  is 
finally  dried  at  100°  C.  If  dried  whilst  containing  water,  it  forms 
a  hard  horny  mass. 

Soldner  showed  that  two  lime  compounds  exist  (CaO  and  2CaO) 
to  one  molecule  of  casein  (C^7oH268N42SP05i). 

Lactalbumin. — This  protein  coagulates  at  70°  C,  although  tlu; 
precipitation  is  never  complete.  Like  other  albumins  it  is  not  pre- 
cipitated by  saturating  its  solutions  with  MgSO^.  It  is  precipitated 
like  other  albumins,  by  saturating  its  solution  with  Na2S04.  Its 
rotatory  power  is  [a]^  =  -  67-5°. 

It  can  be  prepared  by  saturating  milk  with  MgS04,  filtering,  and 
adding  to  the  filtrate  acetic  acid  until  0*25  per  cent,  of  the  solution 
is  reached,  when  lactalbumin  is  precipitated.  It  is  redissolved  in 
water,  again  saturated  with  MgS04,  and  reprecipitated  with  the 
same  strength  of  acetic  acid.  This  treatment  is  repeated  three  or 
four  times.  The  solution  of  lactalbumin  is  next  dialyzed  to  remove 
salts.  When  the  salts  have  been  got  rid  of,  the  solution  is  precipi- 
tated with  alcohol  and  ether,  and  dried  at  a  low  temperature. 
The  result  is  a  tasteless  white  powder  completely  soluble  in  water. 

Lactogflobulin. — This  protein  is  not  coagulated  by  rennet,  but  is 
coagulated  by  heat  and  neutral  sulphates.  It  occurs  in  very  small 
quantities  in  milk,  and  it  is  doubtful  whether  it  is  distinct  from 
serum  globulin. 

Muco-Protein  of  Storch. — This  body  is  insoluble  in  dilute  am- 
monia and  weak  hydrochloric  acid.  It  is  partially  soluble  in  the 
hydroxides  of  potassium  and  sodium,  undergoing  at  the  time  of 
mixture  considerable  increase  in  bulk.  It  gives  the  character- 
istic protein  reactions  with  the  xantho-proteic  and  Millon's  tests. 
On  gently  heating  with  dilute  sulphuric  acid  it  yields  a  reducing 
sugar.  When  washed  with  alcohol  and  ether  and  dried  at  the 
ordinary  temperature  of  the  atmosphere  it  forms  a  light  grejash 
powder  which  is  very  hygroscopic. 

It  may  be  prepared  by  centrifugalizing  separated  milk  and  wash- 
ing the  deposit  with  weak  ammonia-water.  The  resulting  mass  is 
then  well  washed  with  alcohol  and  ether,  and  dried.  Or  it  may  be 
prepared  from  cream.  Storch  has,  by  means  of  benzene,  alcohol, 
and  ether,  separated  it  from  butter. 


152  PRACTICAL  SAXITARY  SCIEXCE 

Milk  contains  traces  of  extractives  and  colouring  matters.  Its 
characteristic  white  appearance  is  held  to  be  due  to  the  interference 
of  light  rays  produced  by  casein  in  pseudo-solution,  a  state  in  which 
particles  exist  in  the  solution  not  of  sufficient  size  to  settle  under 
gravity,  but  which  interfere  with  the  passage  of  light.  These 
particles  can  be  separated  by  a  current  of  electricity.  There  is  no 
sharp  line  of  di\'ision  between  crystalloids  and  colloids  in  solution, 
substances  in  pseudo-solution,  and  bodies  in  suspension.  In  milk, 
fat  is  in  suspension,  casein  in  pseudo-solution,  albumin  in  solution 
as  a  colloid,  and  lactose  in  solution  as  a  crystalloid.  The  variety 
in  size  of  the  particles  or  masses  of  molecules  probably  determines 
tlie  presence  of  one  or  other  of  these  states  in  a  given  case. 

Lactose. — Lactose  (CjoHojOj^HoO)  is  an  aldose,  and  exhibits  the 
constitution  of  a  galactose-glucoside  in  that  on  hydrolysis  by  acids 
it  produces  a  mixture  of  galactose  and  glucose.  The  aldehyde 
group  of  the  galactose  has  been  eliminated  in  lactose,  whilst  the 
glucose  remains. 

Several  modifications  of  milk-sugar  are  known,  distinguishable 
from  each  other  chiefly  by  their  action  on  polarized  light.  Lactose, 
like  other  aldoses  and  ketoses,  reduces  alkaline  solutions  of  CuSOj, 
forming  cuprous  oxide,  the  well-known  Fehling's  reaction.  Each 
sugar  effects  a  definite  amount  of  reduction,  and  this  affords  an 
excellent  method  of  distinguishing  them.  Lactose  differs  from 
other  sugars  in  that  its  osazone  forms  an  anhydride  soluble  in 
boiling  water. 

Lactose  is  hydrolysed  by  a  specific  enzyme  lactose  found  in 
certain  torulfe,  in  some  kefir  preparations,  and  in  aqueous  extract 
of  almonds.  Lactose  is  not  hydrolysed  by  maltose,  invertase,  or 
diastase.  It  easily  undergoes  lactic  and  but\^ric  acid  fermentations. 
Mineral  acids  hydrolyse  it  to  glucose  and  galactose.  It  reduces 
Fehling's  solution,  and  exhibits  mutarotation.  It  is  manufactured 
by  evaporation  of  whey,  the  resulting  crystals  being  purified  by  re- 
crystaHization. 

Fat  of  Milk.- — The  fat  of  milk  consists  of  a  mixture  of  ethereal 
salts  of  glycerol,  forming  small  globules  ranging  in  size  from 
O'OOi  millimetre  to  o-oi  millimetre. 

It  is  highly  probable  that  there  are  three  separate  acid  radicles 
combined  with  each  glycerol  group,  thus : 


MILK 


153 


a  compound  of  the  acid  radicles  of  butyrin,  olein,  and  stearin  with 

glyceryl. 

Milk-fat  has  the  following  composition: 


Per  Cent 

Butyrin 

•          3-90 

Caproin 

•       3-45 

Caprylin 

0-50 

Caprin 

.       1-85 

Myristin 

.     20-30 

Laurin 

•       7-50 

Stearin 

2-00 

Palmitin 

•       25-50 

Olein 

•     35-00 

In  addition  to  the  above  fats,  traces  of  certain  extractives,  such 
as  urea,  lecithin,  cholesterin,  together  with  colouring  matters, 
exist  in  the  fat  of  milk. 

The  vexed  question  of  the  presence  or  absence  of  a  definite  mem- 
brane round  the  fat  globule  will  not  be  discussed  in  this  work.  It 
may  be  stated  in  a  word  that  Bechamp  from  his  studies  of  the 
appearances  found  on  mixing  ether  with  milk  and  of  the  behaviour 
of  milk  towards  certain  stains  has  concluded  that  an  endosmotic 
membrane  exists ;  whilst  Storch  by  his  observations  is  led  to  believe 
that  instead  of  a  definite  membrane  a  muco-protein  capsule  encloses 
the  fat  globule  and  insensibly  shades  off  into  the  surrounding  fluid. 

Human  milk  has  the  following  composition : 


Per  Cent. 

Water 

.  .        88-2 

Fat 

--       3-3 

Casein 

i-o 

Albumin 

0-5 

Lactose 

. .       6-8 

Ash 

0-2 

The  fat  globules  are  smaller  than  those  of  cow's  milk,  ranging 
from  o-oog  to  0-0009  millimetre.  Its  composition  varies  much  more 
than  that  of  cow's  milk.  It  contains  small  quantities  of  citric  acid. 
It  is  almost  always  alkaline. 

When  milk  is  allowed  to  stand  for  a  time,  a  series  of  well-known 


154  PRACTICAL  SAXITARY  SCIEXCE 

changes  succeed  each  other.  The  fat,  the  hglitest  portion,  rises  to 
the  surface  as  cream.  After  a  variable  period,  depending  on  the 
temperature,  presence  of  certain  micro-organisms,  and  other  factors, 
the  milk  becomes  acid  and  separates  into  solid  curd  and  liquid 
whey.  The  principal  agent  in  this  reaction  is  the  B.  lacticns, 
which  converts  lactose  into  lactic  acid.  Other  micro-organisms, 
such  as  the  B.  hiUyricus,  B.  coli  communis,  etc.,  are  also  capable  of 
fonning  acid,  and  thereb}^  curdling  milk.  Rennet  is  used  artificially 
for  bringing  about  the  same  change.  The  curd  consists  of  precipi- 
tated proteins  with  entangled  fat,  and  the  whey  of  water,  lactose,, 
and  salts.  The  cream  of  ordinary  milk  forms  about  lo  per  cent, 
by  volume  of  the  whole. 

The  variations  in  the  composition  of  milk,  even  from  the  same 
animal,  are  due  to  a  number  of  factors,  such  as  the  health  of  the 
animal,  the  age — 3'oung  animals  secrete  less  milk  and  a  product  of 
poorer  quality^ — the  time  that  has  elapsed  from  the  last  milking, 
the  stage  of  milking,  the  breed  of  the  animal,  the  time  that  has 
elapsed  since  previous  parturition,  the  nature  of  the  food  eaten,  etc. 

There  are,  however,  limits  to  these  variations,  and  all  good  milks 
at  all  times  fall  within  these  limits.  Fatty  solids  may  range  from 
2  to  7  per  cent.,  non-fatty  solids  from  8  to  11  per  cent.,  ash  from 
0-6  to  0-9  per  cent.,  cream  from  2  to  25  per  cent.,  specific  gravity 
from  1-027  to  1-037. 

But  it  is  rare  that  the  fatty  solids  fall  below  3  per  cent.,  and  the 
non-fatty  solids  below  8*5  per  cent.,  and  these  figures  are  insisted 
upon  by  law. 

Comparative  analyses  of  various  milks  are  represented  in  the 
following  table: 

Water. 

Cow  . .  . .  . .  87-7 

Human  subject     . .  . .  88-2 

Goat  .  .  . .  .  .  86-0 

Mare  89-8 

Ass  . .  . .  .  .  . .  90-1 

Ewe  . .         . .         . .  79-4 

In  cattle-plague  and  foot-and-mouth  disease  marked  changes 
occur  in  the  milk  of  the  animals  affected.  The  quantity  is  dimin- 
ished, the  curd  separates  out  quickly  on  heating  from  a  pale  blue 
whey,   and  blood  and  pus  corpuscles  are  generally  present.     In 


roteins. 

Fat. 

Lactose. 

Ash. 

3-5 

3-4 

4-6 

07 

1-5 

y^ 

6-8 

0-2 

4-3 

4-6 

4-2 

0-7 

1-8 

i-i 

6-9 

0-3 

1-6 

1-2 

G-5 

0-4 

6-7 

8-6 

4-3 

0-9 

MIIJx  155 

tuberculosis  the  milk  is  not  markedly  affected  except  in  those  rare 
cases  in  which  the  udder  is  extensively  diseased. 


The  Analysis  of  Milk. 

A  chemical  analysis  is  of  service  from  a  public  health  point  of 
view  in  detecting  the  removal  of  fat,  the  addition  of  water,  or  both, 
and  the  presence  of  artificial  colouring  matters  and  preservatives. 
A  bacteriological  examination  is  often  necessary  in  the  investiga- 
tion of  milk-borne  epidemics — such  as  enteric,  diphtheria,  etc. — and 
for  the  detection  of  tubercle  bacilli;  to  obtain  evidence  respecting 
the  healthiness  of  the  udder,  etc.,  of  the  cow;  and  to  measure  the 
general  bacterial  content,  and  especially  the  degree  of  contamina- 
tion from  fascal  matter. 

For  chemical  analysis  the  milk  must  be  fresh,  as  after  standing 
for  a  time  the  lactose  is  transformed  into  lactic  acid,  and  the  non- 
fatty  solids  consequently  diminished. 

Reaction. — The  reaction  is  mostly  alkaline,  sometimes  ampho- 
teric when  litmus  is  used  as  an  indicator.     This  is  due  to  the  pres- 
ence of  NaH2P04  and  Na2HP04,  the  first  turning  blue  litmus  red 
and  the  second  red  litmus  blue. 

Estimation  of  Total  Acidity — Lactic  Acid. — Place  loo  c.c.  of 
the  milk  in  a  beaker,  add  5  c.c.  of  a  o-i  per  cent,  phenolphthalein 
solution,  and  titrate  with  ^  NaOH  until  a  faint  pink  tint  appears. 

It  will  be  found  that  generally  20  c.c.  of  ~  NaOH  is  required; 
each  c.c.  of  the  decinormal  alkali  represents  i  degree  of  acidity. 

If  litmus  be  used  as  indicator  instead  of  phenolphthalein,  a  smaller 
figure  will  be  obtained,  as  the  salts  of  milk  and  carbonic  acid  are 
not  sensibly  acid  to  litmus-paper;  for  this  reason  litmus  may  be  used 
in  roughly  determining  the  quantity  of  lactic  acid.  There  is  no 
good  method  for  quantitatively  estimating  lactic  acid.  When  milk 
is  boiled,  its  acidity  is  diminished. 

Specific  Gravity. — Specific  gravity  is  the  weight  of  unit  volume, 
and  may  be  determined  in  two  ways:  first,  by  finding  the  weight 
of  a  known  volume,  and  second,  by  finding  the  volume  of  a  known 
weight.  The  first  method  may  be  used  by  taking  the  weight  of 
liquid  which  fills  a  vessel  of  known  volume — example,  specific- 
gravity  bottle,  or  Sprengel's  tube.     This  method  may  also  be  used 


156  PRACTICAL  SAXITARY  SCIENCE 

b}'  immersing  a  phmimet  of  known  volume  in  the  liquid,  and  noting 
the  loss  of  weight  due  to  the  displacement  of  the  same  volume  of 
liquid — example,  Westphal's  balance.  The  second  method  is 
applied  by  immersing  a  float  of  known  weight  in  the  liquid,  and 
noting  the  volume  immersed,  which  will  be  equal  to  a  volume  of  the 
liquid  of  the  same  weight  as  that  of  the  float — example,  hydro- 
meters, of  which  the  lactometer  is  a  special  form  used  in  testing  milk. 

In  using  the  specific-gravity  bottle,  which  is  perhaps  the  most 
exact  method,  care  should  be  taken  that  the  bottle  is  clean.  It  is 
well  to  observe  the  ritual  of  subjecting  the  bottle  to  cleansing  with 
weak  acid,  water,  alcohol,  and  ether  on  each  occasion  before  use, 
and  to  weigh  it  direct  from  a  desiccator.  The  bottle  is  first  weighed. 
It  is  then  filled  with  milk,  the  stopper  is  gently  let  in,  and  its  hollow 
channel  is  filled  to  the  top  with  the  fluid.  Any  superfluous  milk 
is  carefully  wiped  away  with  a  clean  and  dr\'  duster,  and  the  bottle 
is  again  deposited  in  the  desiccator  for  a  short  period  before  weigh- 
ing a  second  time.  The  temperature  should  remain  constant  and 
at  15-5°  C.  during  the  entire  process. 

The  second  weight  minus  the  first  is  equal  to  the  weight  of  the 
milk  contained  in  the  bottle.  This  weight  divided  by  the  weight 
of  the  same  volume  of  distilled  water  at  the  same  temperature  is 
the  specific  gravity.  Most  specific-gravity  bottles  have  the  weight 
of  distilled  water  which  they  contain  at  15-5°  C.  marked  on  their 
surface,  so  that  it  is  unnecessary  to  take  this  weight. 

Taking  the  specific  gravity  of  HoO  at  15-5°  C.  as  i-ooo,  that  of 
milk  is  about  1-032.  It  is  obvious  that  the  removal  of  fat  which 
is  the  lightest  constituent  of  milk  raises  the  specific  gravity,  and 
its  addition  lowers  it.  The  addition  of  water  also  lowers  the  specific 
gravity.  So  therefore  a  low  specific  gravity  may  mean  either  abun- 
dant fat  or  added  water. 

The  specific  gravity  of  milk  is  observed  to  rise  slightly  for  some 
hours  after  milking — e.g.,  a  milk  of  specific  gravity  1-031  when 
drawn  from  the  cow  may  in  ten  hours  show  a  specific  gravity  of 
1*032;  this  rise  is  known  as  '  Recknagel's  phenomenon.' 

If  the  quantity  of  cream  as  measured  in  a  cream-tube  reading 
percentages  be  the  normal  10  per  cent,  after  standing  twenty-four 
hours,  and  the  specific  gravity  be  found  low,  it  is  clear  that  water 
has  been  added. 


MILK  157 

-  The  Westphal  balance  consists  of  a  graduated  swinging  arm 
resting  on  a  knife-edge  and  a  glass  plummet  suspended  from  a 
hook  attached  to  one  end  of  the  arm.  The  other  end  of  the  arm 
is  drawn  out  to  a  point  which  when  the  balance  is  adjusted  and 
the  plummet  hangs  in  air  should  rest  exactly  opposite  a  similar 
point  on  the  frame.  Three  riders  are  used  on  the  graduated  arm: 
their  weights  are  wholly  empirical,  and  indicate  hundreds,  tens, 
and  units  respectively. 

The  milk  or  other  fluid  is  poured  into  a  glass  cylinder;  the  arm 
is  raised  or  lowered  by  means  of  a  screw  in  the  upright  support 
until  the  plummet  is  just  completely  reversed,  and  the  riders  are 
so  placed  on  various  divisions  of  the  scale  that  the  points  come  to 
rest  exactly  opposite  each  other.  Supposing  that  in  an  estimation 
the  largest  (as  must  be)  is  suspended  from  the  hook  carrying  the 
plummet,  the  tenth  division  of  the  scale,  and  the  tens  and  units 
riders  rest  on  the  scale  divisions  3  and  2  respectively,  when  the 
point  of  the  swinging  arm  comes  to  rest  at  zero  the  specific  gravity 
will  be  100  X  10  + 10  X  3  +1  X  2  =1-032. 

Lactometers,  special  forms  of  hydrometers,  are  less  accurate  in 
estimating  specific  gravities. 

The  specific  gravity  of  milk  varies  between  1-013  and  1-039. 

By  removal  of  all  the  cream  from  a  milk  of  specific  gravity  1-032, 
the  figure  is  raised  to  1-036.  On  the  other  hand,  by  adding  4  per 
cent,  fat  to  the  same  milk,  the  specific  gravity  is  reduced  to  1-028. 
The  specific  gravity  test  is  not  an  absolute  one,  but  a  useful  pre- 
liminary test.  Like  most  substances,  milk  alters  in  specific  gravity 
with  change  of  temperature.  It  does  not  share,  however,  the 
peculiarity  which  water  possesses  of  attaining  its  maximum  specific 
gravity  at  4°  C.  It  decreases  in  specific  gravity  from  freezing- 
point  (-0-5°  C.)  upwards.  Tables  of  corrections  for  temperature 
have  been  constructed  when  the  determination  is  made  at  tempera- 
tures above  or  below  15-5°  C;  but  it  will  be  sufficiently  exact  to 
add  or  subtract  i  degree  of  specific  gravity  for  every  6  degrees  of 
temperature  registered  above  or  below  15-5°  C. 

The  Fat. — Of  the  many  methods  at  present  in  use  for  the  estima- 
tion of  fat,  the  following  two  are  to  be  recommended,  and  the  first 
is  preferable  to  the  second: 

I.  Adams's  Process.- — In  this  gravimetric  method  the  solvent 


158 


PRACTICAL  SAXITARY  SCIEXCE 


used  for  the  extraction  of  fat  is  ether,  convenient  on  account  of  its 
low  boihng-point  and  heat  of  volatihzation,  its  high  solvent  power 
for  fat,  and  its  miscibilit\-  witli  water. 


When  milk  is  dropped  on  blotting-paper,  it  spreads  out  to  a  much 
greater  degree  than  when  placed  on  glass  or  in  a  dish,  and  Adam 


MILK  T59 

considered  that  extraction  of  the  fat  by  etli(;r  would  accord- 
ingly be  much  more  complete.  After  passing  through  various 
stages  of  evolution,  the  process  is  now  carried  out  somewhat  as 
follows : 

A  strip  of  Schleicher  and  Schiill's  fat-free  paper  is  hung  up  by 
one  end.  The  other  end  is  held  in  the  fingers  so  that  the  surface 
of  the  strip  is  as  nearly  as  possible  horiziontal,  and  5  c.c.  of  the  sample 
of  milk  carefully  measured  in  a  pipette  are  distributed  over  the 
paper.  The  weight  of  this  volume  is  determined  by  running  into 
a  convenient  weighing  vessel  5  c.c.  of  the  same  sample  at  the  same 
rate  as  it  was  run  on  to  the  paper.  The  paper  is  allowed  to  hang 
until  dry,  and  must  be  protected  from  flies  and  all  other  disturbing 
influences.  When  dry  the  paper  is  rolled  up  into  a  loose  coil  of 
a  diameter  such  that  it  will  easily  pass  into  the  Soxhlet  extractor 
(say  I  inch).  A  blank  coil  containing  no  milk  should  be  dried  and 
rolled  up  in  the  same  way,  and  both  further  dried  at  100°  C.  for 
an  hour.  Each  coil  is  then  placed  in  a  Soxhlet  extractor,  arranged 
in  an  upright  position,  and  connected  with  vertical  condensers. 
Small  weighed  flasks  of  150  c.c.  capacity  containing  dry  ether  in 
sufficient  quantity  to  fill  the  extractor  well  a]>ove  the  upper  portion 
of  the  siphon,  are  attached  to  the  lower  end  of  the  Soxhlet  apparatus, 
and  the  ether  is  made  to  boil  by  immersing  the  flask  in  water  at 
55°  to  60°  C.  Extraction  should  be  continued  for  two  to  three 
hours,  although  many  analysts  are  satisfied  with  twelve  to  eighteen 
siphonings. 

The  flasks  containing  ether  and  dissolved  fat  are  then  discon- 
nected, the  ether  is  driven  off  by  evaporation,  and  the  flasks  dried 
and  weighed. 

The  difference  in  weight  represents  the  fat ;  the  small  amount  of 
extract  derived  from  the  paper  of  the  blank  experiment  is  finally 
subtracted  from  the  weight  of  fat  found  for  the  sample,  and  the 
difference  represents  the  fat  contained  in  5  c.c.  The  weight  of 
5  c.c.  has  been  determined;  accordingly  the  percentage  of  fat  is 
readily  calculated. 

Sour  milk  may  be  operated  on  if  the  acidity  be  neutralized  by 
—Q  NaOH,  using  litmus  as  indicator. 

It  is  advisable  to  put  a  small  piece  of  blotting-paper  in  the  mouth 
of  the  open  tube  at  the  top  of  the  condenser  so  as  to  limit  the 


i6o  PRACTICAL  SAXITARY  SCIEXCE 

entrance  of  moist  air  which  would  shghtl\'  wet  the  ether.  In  driving 
off  the  ether  from  a  flask,  it  is  well  to  lay  the  flask  on  its  side  in  one 
of  the  openings  of  the  water-bath,  and  afterwards,  when  the  drj-ing 
is  being  completed  in  an  air  oven,  the  flask  should  be  rotated  from 
time  to  time,  and  air  blown  in  every  fi\'e  minutes,  to  remove  ether 
\-apour. 

Dr3''  ether  is  prepared  by  washing  commercial  ether  with  water, 
shaking  the  washed  ether  with  calcium  chloride,  and,  after  allowing 
it  to  stand  over  calcium   chloride  for  a   day  or  two,   distilling. 


A,  Evaporating  basin;  B,  specific-gravity  bottle;  C,  fat  flask;  D,  pipette; 
E,  boiling-tube;  F,  loo  c.c.  stoppered  cylinder. 

Sufficiently  dry  ether  may  also  be  obtained  for  most  purposes  by 
distilling  the  commerical  variet}^  and  rejecting  the  first  fractions 
which  pass  over  below  34-3°  C,  and  the  last  above  34-8°  C. 

If  at  anv  time  doubt  exists  as  to  the  completion  of  the  extraction 
process,  a  second  weighed  flask  containing  fresh  ether  should  be 
afiixed,  and  the  process  continued  for  some  time.  This  flask  after 
evaporating  the  ether  and  drying  at  loo'^  C.  should  not  increase  in 
weight. 

2.  The  Werner-Schmidt  Method. — The  specific  gravity  of  the 
sample  is  ascertained  or  a  measured  volmne  is  weighed.    Fifteen  c.c. 


MILK  i6i 

are  pipetted  into  a  boiling-tube  and  a  like  measure  of  pure  hydro- 
chloric acid  added.  The  mixture  is  shaken  up  and  gently  boiled 
until  the  contents  appear  dark  brown  in  colour.  The  boiling  must 
not  be  continued  too  far,  as  certain  bodies  soluble  in  ether  are  liable 
to  be  formed  from  the  milk-sugar.  The  process  is  not  suitable  for 
milks  containing  cane-sugar.  Boiling  with  acid  renders  the  casein 
soluble,  and  so  eliminates  the  obstacles  which,  in  the  solid  condition, 
it  offers  to  the  extraction  of  fat. 

When  cold,  pour  the  contents  of  the  tube  into  a  graduated 
and  stoppered  lOo  c.c.  cylinder.  Wash  out  the  tube  with  ether, 
and  finally  make  the  column  up  to  75  c.c.  with  ether.  Invert  the 
cylinder  several  times,  and  put  aside  to  settle.  Read  the  height  of 
the  ethereal  column,  including  three-fourths  of  the  thin  grey  layer 
of  casein.  Draw  off  an  aliquot  part  of  this  column  and  evaporate ; 
dry,  and  weigh  the  residual  fat  in  a  small  flask,  in  the  manner 
described  in  Adams's  process. 

-Stokes's  tube,  a  specially  graduated  tube  prepared  to  treat 
10  c.c.  of  milk,  is  also  employed  in  this  country.  After  completing 
the  boiling  with  10  c.c.  of  HCl,  and  cooling,  ether  is  added  until  the 
surface  of  the  column  reaches  the  50  c.c.  mark.  An  aliquot  portion 
of  this  column  is  afterwards  drawn  off,  evaporated,  dried,  and  the 
residue  weighed  as  above.  The  special  tube  is  not  to  be  recom- 
mended, as  the  narrowed  central  portion  offers  resistance  to  the 
free  escape  of  hot  air  during  boiling,  and  the  consequent  explosive 
action  frequently  causes  loss  of  the  contents. 

This  process  is  much  more  rapid  than  that  of  Adams,  and  in 
skilled  hands  almost  as  accurate. 

The  student  will  remember  that,  owing  to  the  low  boiling-point 
of  ether,  it  should  never  be  added  to  a  hot  solution,  and  will  accord- 
ingly always  cool  the  boiling-tube  before  adding  it.  This  may 
be  rapidly  done  by  holding  it  under  a  water-tap.  In  drying  and 
weighing  the  fat  it  is  essential  that  the  last  trace  of  ether  vapour 
be  got  rid  of  by  blowing  dry  air  into  the  flask,  and  by  ascertaining 
that  two  successive  weighings,  separated  by  half  an  hour's  heating 
at  100°  C,  are  the  same. 

Example. — A  milk  whose  specific  gravity  is  1-032  is  subjected 
to  the  Adams  process,  and  the  fat  collected  in  a  flask  weighing 

II 


102  PRACTICAL  SAXITARY  SCIENCE 

16-056  grammes.     The  weight  of  the  flask  and  fat  is  16-236  grammes. 
The  weight  of  the  fat  is  therefore  o-i8o  gramme. 

5  c.c.  of  specific  gravity  1-032  =5-16  grammes. 

If  now  5-16  grammes  of  milk  yield  o-iS  gramme  fat,  what  is  the 
percentage  of  fat  ? 

5-16  :  100  :  :  o-i8  :  the  percentage. 
Percentage  therefore  =3-5  nearly. 

The  same   sample   subjected  to   the   Werner-Schmidt   process 
yielded  practically  the  same  result. 

15  c.c.  of  the  milk  yielded  0-542  gramme  fat; 
but  15  c.c.  of  specific  gravity  1-032  =15-48  grammes; 
15-48  :  100  :  :  0-542  :  3-5. 

3.  There  are  several  forms  of  centrifugal  apparatus  used  for  esti- 
mating fat,  such  as  the  Babcock,  Leffmann-Beam,  Gerber,  etc. 

The  Leffmann-Beam  provides  small  flasks  graduated  on  the  neck 
into  eighty  divisions — ten  divisions  corresponding  to  i  per  cent,  of 
fat.  Run  into  the  flask  15  c.c.  milk.  Add  3  c.c.  of  a  mixture  of 
equal  parts  HCl  and  amyl  alcohol;  shake  and  add  slowly  with 
agitation  9  c.c.  concentrated  H.^SOj.  Fill  up  to  2iero  with  hot  mix- 
ture of  equal  parts  concentrated  H0SO4  and  water.  Place  in  the 
centrifuge  and  rotate  for  two  minutes.  If  fat  and  acid  liquid  are 
both  quite  clear,  read  off  the  fat  column;  if  fat  or  acid  liquid  be 
cloudy,  rotate  again.  The  amyl  alcohol  assists  in  the  collection  of 
the  fat  globules:  this  reagent  should  be  good,  otherwise  large  error 
may  occur,  generally  in  the  direction  of  excess  of  the  truth.  Where 
the  operation  is  carefully  carried  through  with  sound  reagents  results 
are  obtained  to  within  0-15  per  cent,  of  those  got  by  the  Adams's 
process. 

The  reagents  used  in  the  Gerber  process  are  H.,SOj  and  amyl 
alcohol.  The  centrifuge  runs  on  ball  bearings,  and  reaches  a  velocity 
of  about  2,000  revolutions  per  minute.  Three  minutes  are  sufficient 
to  separate  the  fat. 

In  the  Babcock  method  H^SOj  and  boiling  water  are  employed 
as  reagents.     The  centrifuge  revolves  at  about  1,000  times  per 


MILK  163 

minute — hence  a  longer  time  is  required  for  completing  the  separa- 
tion of  fat  (seven  to  eight  minutes). 

These  centrifugal  methods  are  used  for  determining  the  fat — 
(i)  in  condensed  milk  after  it  has  been  diluted  to  form  a  10  per 
cent,  solution ;  (2)  in  cream  after  it  has  been  diluted  five  or  six  times 
with  hot  water;  (3)  in  butter  and  (4)  in  cheese  after  mixture  with  a 
small  quantity  of  cold  or  hot  water,  as  suitable,  by  addition  of 
modified  quantities  of  the  reagents,  and  the  necessary  rotation. 

Estimation  of  Cream.^ — A  cream-tube  or  creamometer  provided 
with  a  short  scale  at  its  upper  part,  each  division  of  which  reads 
I  per  cent,  of  the  capacity  of  the  tube  up  to  the  highest  line  (^ero), 
is  filled  to  the  zero  with  the  milk  to  be  tested,  and  set  aside  for  six, 
twelve,  or  twenty-four  hours,  and  the  volume  of  cream  measured. 
A  good  milk  should  throw  up  10  per  cent,  of  cream  in  eight  hours. 
The  method  is  by  no  means  accurate,  as  the  same  milk  under 
different  conditions  of  setting  may  show  very  marked  differences 
in  the  quantity  of  cream  formed. 

The  estimation  of  fat  in  dried  milk  may  be  made  by  the  Wernef- 
Schmidt  method  or  by  the  Rose-Gottlieb  method,  preferably  the 
latter. 

Rose-Gottlieb  Method. — Weigh  0-5  gramme  milk  powder  into  a 
stoppered  cylinder  holding  about  50  c.c.  Add  5  c.c.  water  and 
0*5  c.c.  ammonia  (equal  parts  o-88  ammonia  and  water).  Shake 
and  warm  if  necessary  until  solution  is  obtained.  Add  5  c.c. 
alcohol  and  shake  again  until  homogeneous.  Now  add  12-5  c.c. 
ether  and  mix  very  thoroughly;  finally  add  12-5  c.c.  petrolemn  ether 
(boiling  below  60°  C.)  and  again  mix  thoroughly.  Settle  out  and 
draw  off  the  ether.  Repeat  the  extraction  with  a  mixture  of  equal 
parts  ether  and  petroleum  ether  until  the  whole  of  the  fat  is  re- 
covered. Remove  the  solvent  by  distillation,  dry,  and  weigh  the 
fat. 

Total  Solids. — Pipette  into  a  clean,  weighed,  platinum  dish 
10  c.c.  of  the  milk,  and  reweigh  to  obtain  the  weight  of  the  milk 
used.  Heat  on  a  water-bath,  breaking  up  occasionally  the  film 
that  forms  on  the  surface,  in  order  to  hasten  evaporation.  After 
an  hour's  drying,  the  dish  is  removed  to  a  tray,  carrying  two  or 
three  layers  of  blotting-paper  to  remove  moisture,  and  the  tray 
is  placed  in  an  air  oven  at  a  temperature  of  95°  C,  and  provided 


i64  PRACTICAL  SANITARY  SCIENCE 

with  sufficient  draught;  here  the  drying  is  completed.  It  ma^'' 
require  two  to  three  hours  in  the  oven  to  produce  a  constant  weight. 
Platinum  basins  are  preferable  to  porcelain,  as  the}^  cool  much 
more  rapidly,  and  thus  require  less  time  in  the  desiccator.  As  milk 
solids  are  highly  hygroscopic,  no  time  must  be  lost  in  conveyance 
from  the  desiccator  to  the  balance,  nor  in  the  process  of  weighing. 
Supposing  that  the  specific  gravity  of  the  milk  is  1-032,  the  weight 
of  10  c.c.  will  be  10-32  grammes.  Further,  supposing  the  difference 
in  the  first  and  second  weighings  of  the  dish  to  be  1-3  grammes, 
the  percentage  of  total  solids  will  be  found  from  the  proportion : 

10-32  :  100  :  :  1-3  :  x  ; 
100  X  1-3 
10-32  ^ 

From  the  total  solids  the  ash  is  obtained  by  ignition  at  a  low 
heat  over  an  argand  burner.  The  last  trace  of  dark,  separated 
carbon  must  disappear  and  the  residue  consist  of  a  greyish-white 
mass  before  the  dish  is  removed  from  the  flame.  Overheating 
causes  loss  of  NaCl.  Cooling,  weighing,  and  percentage  calculation 
are  carried  out  in  the  usual  manner. 

TheP  and  S  of  the  milk  proteins  produce  phosphoric  and  sulphuric 
acids.  Carbonic  acid  is  formed  by  the  combustion  of  organic 
carbon.  The  ash  does  not  truly  represent  the  inorganic  consti- 
tuents. It  is  computed  that  at  least  8  per  cent,  of  the  phosphoric 
acid  arises  from  the  P  of  the  casein.  Bases  predominate  over  acids 
in  milk,  and  unite  with  proteins  to  fomi  soluble  protein  salts,  and 
with  citric  acid  to  form  citrates. 

Composition  of  ash: 


Per  Cent. 

Lime  . .  . .  . .  . .     19-3 

Phosphoric  acid 

Potash 

Chlorine 


Soda 

Ferric  oxide  . . 

Magnesia 

Carbonic  acid 

Sulphuric  acid 


28-3 

277 

13-9 
6-7 

0-3 
27 

I'D 
O-I 


A  probable  composition  for  the  salts  as  they  exist  in  milk  has 
been  theoretically  calculated: 


MILK 


i<>5 


Per  Cent. 

NaCl 

.        10-62 

KCl 

9-16 

KH0PO4       . . 

.        1277 

K2HPO4       . . 

9-22 

KsfCeH^O,)  .  . 

■      5-47 

MgHPO^      . . 

.       371 

Mg3(CeH,0,) 

•      4-05 

CaHPO^        . . 

•      7-42 

Ca3(P04)2     . . 

8-90 

CagiCeHgO^)., 

•     23-55 

Lime  combined  with  proteins  . 

•       5-13 

ash  is  materially  less  than  073 

per  cent. 

,  watering  may  be 

suspected. 

Solids  not  Fat. — This  item  of  the  analysis  is  calculated  by  finding 
the  difference  in  weight  between  the  total  solids  and  the  fat.  The 
solids  not  fat  have  been  found  to  vary  between  5  and  10  per  cent. 
The  law  fixes  8-5  as  the  lower  limit  for  whole  milk. 

In  case  it  is  necessary  to  determine  the  percentage  of  proteins 
in  milk,  the  best  method  to  employ  is  the  following  modification  of 
Kjeldahl's  method  for  the  estimation  of  total  organic  nitrogen,  and 
multiply  the  result  by  6-38.  To  obtain  the  total  organic  nitrogen, 
weigh  5  grammes  of  milk  into  a  Kjeldahl  flask  of  about  150  c.c. 
capacity,  and  add  20  c.c.  pure  H2SO4.  Place  over  a  small  flame  in 
the  fume-chamber,  and  heat  till  thoroughly  charred.  Remove  the 
flame,  and  add  10  grammes  bisulphate  of  potash  to  raise  the  boiling- 
point  of  the  mixture.  Place  a  pear-shaped  bulb  in  the  neck  of  the 
flask  and  apply  the  flame,  increasing  its  siz;e  as  frothing  ceases.  The 
liquid  becomes  colourless  in  thirty  minutes  or  thereabouts.  Cool, 
dilute  largely  with  water,  and  transfer  to  the  distillation-flask  pro- 
vided with  perforated  cork  carrying  a  dropping  funnel  with  stop- 
cock, and  a  wide  tube  with  one  or  more  bulbs  blown  in  it,  which 
are  loosely  packed  with  asbestos.  One  end  of  the  tube  is  connected 
with  a  condenser,  and  the  other  is  made  to  dip  below  the  surface  of 
50  c.c.  i\  H2SO4. 

Through  the  dropping-funnel  pass  about  100  c.c.  of  a  20  per  cent, 
solution  of  NaOH.  Shake  well  by  a  rotatory  motion.  Apply  a 
flame  to  the  distilling-flask  and  collect  about  200  c.c.  of  the  dis- 
tillate. Take  care  that  the  condenser  remains  throughout  quite 
cold.     Titrate  with  y^  NaOH,  using  litmus  as  indicator.     Subtract 


166  PRACTICAL  SAXITARY  SCIEXCE 

the  number  of  c.c.  -i^g-  XaOH  solution  used  from  the  50  c.c.  ^c- 
sulphuric  acid,  and  the  remainder  represents  the  acid  neutralized 
by  the  ammonia  distilled  over.  From  this  deduct  the  figure  ob- 
tained in  a  blank  experiment  in  which  all  the  factors  are  exactly  the 
same,  except  that  milk  is  eliminated. 

Each  c.c.  of  the  j\y  H2SO4  neutralized  by  ammonia  is  equal  to 
0-0014  gramme  of  X,  which,  when  multiplied  by  6"3S,  is  equal  to 
the  total  protein. 

Colostrum  is  a  term  applied  to  the  first  milk  secreted  after  par- 
turition. Hi)udet  describes  two  forms — a  viscous,  brownish  product, 
and  a  non- viscous  lemon-yellow  liquid;  the  earlier  milkings  furnish 
the  first,  and  the  later  the  second;  the  two  co-exist  often  in  the 
same  animal.  The  fat  differs  somewhat  from  that  of  ordinar\'  milk, 
in  that  its  melting-point  is  high  (42°  C.)  and  its  Reichert-WoUny 
figure  low  (6  to  7).  The  most  characteristic  feature  of  colostrum 
is  the  presence  of  the  corps  granuleux  of  Donne,  consisting  of  cells 
clustered  together  like  bunches  of  grapes,  and  measuring  in  diameter 
from  0-005  to  0-025  millimetre.  The  specific  gravity  of  colostrum 
averages  i-o68. 

Estimation  of  Citric  Acid  in  Milk. — Prepare  acid  nitrate  of  mer- 
cur}'  by  dissoh'ing  mercur}"  in  twice  its  weight  of  HXO3  (specific 
gravity  1-42),  and  adding  an  equal  volume  of  water. 

With  this  reagent  precipitate  the  proteins  of  the  milk,  and  filter 
until  the  filtrate  is  clear.  Rapid  clearing  may  be  effected  at  this 
stage  by  addition  of  some  super-saturated  solution  of  aluminium 
hvdrate.  To  a  measured  volume  of  the  filtrate  add  dilute  caustic 
soda  solution  until  the  neutral  point  is  reached  (phenolphthalein  as 
indicator).  Filter  off  the  white  precipitate  of  calcium  phosphate, 
calcium  citrate,  and  mercuric  nitrate ;  wash  well  with  water ; 
remove  from  the  filter,  and  suspend  in  water,  to  which  a  little 
dilute  HCl  has  been  added.  Pass  HoS  through  the  fluid  until 
all  the  mercury  comes  down  as  HgS.  Filter  again,  and  boil  the 
filtrate  to  remove  H^S.  Add  a  little  calcium  chloride  and  cool. 
Carefully  neutralize  a  second  time  with  dilute  caustic  soda,  and 
filter  off  the  calcium  phosphate.  Concentrate  the  filtrate  to  small 
bulk.  This  contains  the  citric  acid  as  calcium  citrate.  After 
thorough  boiling,  filtering,  and  washing  the  precipitate  with  boiling 
water,  ignite  it,  and  add  to  it  excess  -j^g-  HCl.     Titrate  back  the  excess 


MILK  167 

with  ~Q  NaOH  (methyl  orange  as  indicator).  Each  c.c.  -^^^  HC 
used  =0-007  gramme  citric  acid. 

Action  of  Heat  on  Milk. — When  heated  to  70"  C,  the  albumin 
of  milk,  although  not  precipitated,  is  so  changed  that  it  is  readily 
precipitated  by  acids  and  MgSO^.  At  80"  C.  a  further  unknown 
change  occurs  in  certain  organic  constituents,  recognizable  by  the 
fact  that  they  cease  to  evolve  a  gas  from  HgOg,  and  to  produce  a 
blue  colour  with  paraphenylenediamine  and  H2O2. 

Test  for  Boiled  Milk.—SYvake  5  c.c.  milk  in  a  test-tube  with  i  drop 
of  a  2  per  cent.  H2O2  solution  and  2  drops  of  a  2  per  cent,  para- 
phenylenediamine solution.  If  the  milk  has  not  been  heated  above 
80°  C,  a  dark  violet  or  blue  colour  appears  at  once;  but  if  it  has 
been  boiled  or  pasteurized  to  this  temperature,  no  colour  appears. 
At  100°  C.  calcium  citrate  is  deposited,  and  a  reduction  in  the 
rotatory  power  of  milk-sugar  takes  place. 

When  milk  is  heated  in  contact  with  air  a  pEotein  film,  probably 
an  oxidation  product,  is  formed  on  the  surface,  which  has  been 
variously  classified. 

It  has  been  claimed  that  boiled  milk  is  more  easy  of  digestion 
than  the  raw  secretion,  and  perhaps  this  is  true.  The  much-dis- 
cussed question  of  boiled  milk  producing  symptoms  of  scurvy  has 
not  been  settled;  there  is  no  reliable  evidence  from  which  a  con- 
clusion may  be  drawn. 

Lactose.- — An  important  product  of  milk  in  connection  wath  the 
artificial  feeding  of  infants  is  milk-sugar.  Its  estimation  may  be 
carried  out  as  follows : 

To  50  c.c.  distilled  water  add  6  grammes  of  milk-sugar  finely 

powdered,  and  stir  with  a  thermometer  for  ten  seconds;  allow  to 

settle  for  twenty  seconds,  and  read  the  fall  in  temperature.     Filter, 

and  fill  a  polariscope  tube  with  the  clear  filtrate.     Take  readings 

every  minute  until  the  specific  rotatory  power  begins  to  diminish. 

When  the  polarized  solution  is  kept  at  a  temperature  of  15°  C, 

several  readings  can  be  obtained  which  are  nearly  constant;  the 

mean  of  these  is  the  initial  rotation.     After  twenty-four  hours, 

polarize  again  at  the  same  temperature  to  obtain  the  normal  rota- 

^,      initial  rotation  .,,,,. 

tion.     Ihe \ — TT^- —  IS  the    birotation  ratio. 

normal  rotation 

The  amount  of  sugar  may  be  estimated  in  100  c.c.  of  the  above 


1 68  PRACTICAL  SANITARY  SCIEXCE 

solution  by  dividing  the  normal  rotation  reading  in  angular  degrees 
by  i-io6. 

Principles  of  Polarimetry. — The  vibrations  which  constitute  an 
ordinary  light  ray  take  place  in  all  directions  in  a  plane  perpendicu- 
lar to  the  line  of  propagation  of  the  ray.  If  one  looks  at  an  object 
through  a  crystal  of  Iceland  spar,  two  images  are  seen — the  light 
ray  has  been  split  by  the  crystal  into  two,  the  more  refracted  or 
ordinary  ray,  and  the  less  refracted  or  extraordinary  ray.  The  less 
refracted  or  extraordinary  ray  does  not  obey  the  ordinary  laws  of 
refraction,  but  presents  an  image  which  moves  when  the  crystal 
is  rotated.  Both  rays  are  said  to  be  polarised — i.e.,  consist  now 
of  vibrations  in  one  direction  only  in  the  plane  perpendicular  to  the 
line  of  propagation  of  the  ray. 

If  a  crystal  of  spar  be  cut  through  its  obtuse  angles,  the  sections 
polished  and  cemented  together,  and  the  long  sides  blackened,  a 
Xicol  prism  is  formed.  Such  a  prism  absorbs  the  ordinary  ray 
by  the  black  sides  after  it  has  been  totally  reflected  by  the  cut 
surfaces,  whilst  it  allows  the  extraordinary  ray  to  pass  through  in 
a  direction  parallel  to  the  source  of  light. 

A  polarimeter  consists  of  two  Nicols  mounted  parallel  to  each 
other — one,  the  polarizer,  fixed;  the  second,  the  analyijer,  movable. 
If  the  movable  prism  is  exactly  parallel  to  the  fixed,  a  beam  of  light 
will  pass  through  it;  if  not  exactly  parallel,  but  inclined  at  an  angle, 
less  light  will  pass  through;  if  at  right  angles,  all  light  will  be  cut  off. 

If  a  solution  of  an  optically  active  substance  be  interposed  be- 
tween the  Xicols  set  parallel,  the  quantity  of  light  passing  through  is 
diminished,  but  the  original  intensity  can  be  recovered  by  rotating 
the  analyzing  prism.  The  amount  of  such  rotation  is  equal  to  the 
power  of  rotation  of  the  solution.  In  all  polarimeters  the  analyzer 
is  mounted  on  a  graduated  circle,  so  that  the  number  of  degrees  of 
rotation  can  be  easily  measured. 

The  recognition  of  equal  intensity  of  light  in  a  polarimeter  before 
and  after  the  passage  of  light  through  an  optically  active  solution  is 
very  difficult,  and  readings  are  accordingly  far  from  correct.  To 
overcome  this  difficulty,  Laurent  placed  behind  the  polarimeter  a 
quartz  plate  of  such  thickness  that  one  of  the  two  light  rays  pro- 
duced in  it  is  retarded  by  half  a  wave  length  (and  consequently 
reversed  in  direction),  and  of  such  size  tha.t  it  covered  half  the  field. 


MILK  169 

The  ray  resulting  from  the  blending  of  the  affected  and  unaffected 
rays  accordingly  emerges  in  a  plane  at  an  angle  to  the  original 
plane;  in  other  words,  the  polarized  light  passing  through  the 
quartz  plate  is  rotated  through  an  angle.  Two  sets  of  rays  of 
polarized  light  at  an  angle  to  each  other  will  accordingly  reach  the 
analyzer.  If  the  analyzer  be  arranged  parallel  to  the  light  coming 
from  the  covered  portion,  this  half  of  the  field  will  appear  Hght,  and 
the  other  half  dark.  On  the  contrary,  if  the  analyzer  be  set  parallel 
to  the  light  coming  from  the  uncovered  portion,  this  half  of  the  field 
will  appear  light,  and  the  other  half  dark.  By  adjustment  the 
analyzer  can  be  placed  in  a  position  in  which  the  two  halves  appear 
equally  illuminated.  This  position  corresponds  with  the  zero  of 
the  circular  scale  and  with  the  zero  of  the  vernier.  With  Laurent's 
polarimeter  monochromatic  sodium  light  is  used,  a  cell  containing 
potassium  bichromate  being  placed  in  front  of  the  polarizer  to 
intercept  the  blue  rays. 

The  instrument  consists  of  the  following  parts:  Bichromate  cell, 
polarii^ing  prism,  quartz  plate  covering  half  field,  trough  to  carry 
solution  under  examination,  circle  graduated  in  degrees,  a  double 
vernier  attached  to  analyzing  prism  and  moving  on  graduated  circle, 
and  a  telescope  to  focus  edge  of  quartz  plate. 

When  the  active  substance  in  solution  is  placed  between  the 
Nicols  and  equal  illumination  of  the  two  half  fields  restored,  the 
vernier  will  have  moved  in  the  direction  of  the  hands  of  a  clock 
(dextro-rotatory),  or  in  the  opposite  direction  (laevo-rotatory) . 
The  distance  traversed  measured  on  the  circular  scale  gives  the 
amount  of  rotation  in  degrees. 

The  specific  rotatory  power  [a]^- — that  is,  the  rotation  produced 
by  I  gramme  of  the  substance  dissolved  in  i  c.c.  of  liquid  examined 
in  a  tube  i  decimetre  long  (rotatory  power  of  100  per  cent,  solution) 
— being  known,  we  can  determine  the  strength  of  an  unknowm 
solution. 

For  glucose  [a]D=+52-5°;  lactose +  52-4°;  sucrose +  66°;  galac- 
tose  +  82°;  maltose +  1377°;  fructose  — 93-8°  at  20°' C. 

The  percentage  strength  of  a  solution  is  given  by  the  formula- — 

ax  100 


170  PRACTICAL  SAXITARY  SCIEXCE 

where  [a]„  =specilic  rotation  for  sodium,  or  D  light, 
a     =  observed  rotation  on  the  circular  scale, 
c      =  concentration. 
1      =  length  of  tube  in  decimetres. 

Polarimetric  Estimation  of  Lactose  in  Milk.— Put  60  c.c.  milk 
in  a  100  c.c.  flask;  add  i  c.c.  mercuric  nitrate  (Hg  dissolved  in  twice 
its  weight  of  HNO3,  specific  gravity,  1-42  + an  equal  volume  of 
H.,0),  and  fill  up  to  the  mark  with  water.  Shake  thoroughly  and 
filter  through  a  moist  filter-paper.  When  quite  clear,  determine 
rotation  in  polarimeter.  ^lake  several  readings,  and  take  an 
average.  Correct  for  space  occupied  by  proteins  and  fat.  The 
volume  of  the  fat  in  c.c.  is  found  by  estimating  its  weight  and 
multiplying  by  1-075,  and  the  volume  of  the  proteins  is  found  by 
multiplying  their  weight  by  o-S.  Water  equal  to  the  sum  of  these 
volumes  in  c.c.  is  added  to  the  100  c.c. 

The  calculation  involved  by  taking  60  c.c.  of  milk  may  be  avoided 
by  taking  a  simple  multiple  of  the  standard  amount  of  the  polari- 
meter used.  Thus,  in  the  case  of  an  instrument  adjusted  so  that 
20-56  grammes  lactose  in  100  c.c.  of  solution  produce  100  degrees 
on  the  percentage  scale,  61*68  grammes  (20-56x3)  are  weighed, 
treated  with  mercuric  nitrate  solution,  and  made  up  to  100  c.c. 
The  volumes  of  fat  and  proteins  are  calculated,  and  the  sum  added 
to  the  100  c.c.  Finall}'  the  polarimeter  reading  divided  by  3  will 
give  the  percentage  of  hydrated  lactose. 

Estimation  by  Fehling-'s  Method. — This  method  depends  on  the 
fact  that,  whilst  Fehling's  solution  may  be  boiled  without  change 
if  a  small  quantity  of  glucose  or  other  reducing  sugar  be  added 
at  the  boiling  temperature,  a  precipitate  of  cuprous  oxide  is  formed, 
and  that  the  amount  of  copper  salt  reduced  is  proportional  to  the 
quantity  of  sugar  used.  Prepare  Fehling's  solution.  Powder  and 
press  between  blotting-paper  to  remove  moisture  crystals  of  pure 
copper  sulphate  (CuS04,5H20) ;  weigh  69*28  grammes;  dissolve  in 
water;  add  0-5  to  i  c.c.  pure  H2SO4;  dilute  with  pure  water  to  a  litre. 
Weigh  350  grammes  Rochelle  salt 

/  CH  (OH) -COOK  \ 

I  sodium  potassium  tartrate  1  ) 

\  CHOH-COONa,4H20/ 

and  dissolve  in  about  700  c.c.  water;  weigh  100  grammes  NaOH 


MILK  171 

prepared  with  alcohol;  dissolve  in  aljout  200  c.c.  pure  water,  mix 
the  solutions,  and  make  up  to  a  litre. 

These  two  solutions  are  kept  separate,  and  mixed  in  equal  pro- 
portions immediately  before  use.  Each  c.c.  of  the  mixture  should 
contain  0-03464  gramme  cupric  sulphate,  which  corresponds  with 
0-005  gramme  anhydrous  grape  sugar  and  0-006786  gramme  lactose. 

For  estimation  of  lactose,  Pavy's  modified  Fehling  process  is 
preferable.  Pavy  added  ammonia  to  the  ordinary  Fehling  solution 
to  prevent  the  precipitation  of  cuprous  oxide.  The  end  reaction  is 
fixed  by  the  disappearance  of  the  blue  colour  in  a  perfectly  clear 
solution. 

Mix  120  c.c.  ordinary  Fehhng  (not  100  c.c,  because  in  ammoniacal 
solution  only  5  molecules  CuO  are  reduced  by  one  molecule 
glucose,  instead  of  6  CuO)  with  300  c.c.  ammonia  (specific  gravity, 
0-88);  add  100  c.c.  10  per  cent.  NaOH  or  14  per  cent.  KOH,  and 
make  up  to  a  litre,  [i  c.c.  =0-0005  gramme  glucose  and  0-0006786 
gramme  lactose.]  A  little  more  time  should  be  allowed  during 
titration  for  the  reduction,  as  Pavy's  solution  acts  more  slowly  than 
the  ordinary  Fehhng,  but  the  operation  should  be  completed  within 
three  or  four  minutes,  otherwise  the  ammonia  disappears  and  CugO 
is  deposited. 

Weigh  25  grammes  milk  into  a  250  c.c.  flask;  add  h,  c.c.  of  a 
30  per  cent,  solution  of  acetic  acid;  shake  well,  and  stand  aside  for 
a  few  minutes.  Dilute  with  about  100  c.c.  boiling  water,  and  add 
25  c.c.  alumina  cream;  shake  and  set  aside  again.  Pour  the  more 
or  less  clear  liquid  through  a  wet  filter,  and  finally  wash  out  on  the 
filter  the  entire  contents  of  the  flask.  Collect  the  filtrate,  w^hich 
must  be  perfectly  clear,  and  make  up  with  water  to  250  c.c. 

Transfer  a  portion  of  the  clear  sugar  solution  to  a  burette. 
Raise  to  the  boiling-point  in  a  porcelain  dish  10  c.c.  of  the  Pavy- 
Fehling  solution.  Run  in  the  sugar  solution  (drop  by  drop  if 
possible  towards  the  end)  until  the  last  trace  of  blue  disappears. 
The  number  of  c.c.  delivered  from  the  burette  =0-006786  gramme 
lactose.     From  this  calculate  the  percentage. 

If  the  ordinary  Fehling  method  be  used,  a  difficulty  is  encountered 
in  determining  the  end-point — i.e.,  the  instant  at  which  the  blue 
colour  is  completely  discharged.  Dilution  of  the  sugar  solution 
with  very  weak  NaOH  causes  the  CU2O  to  separate  out.     If  soda 


172  PRACTICAL  SAXITARY  SCIENCE 

be  used  in  very  large  excess,  the  oxide  is  kept  in  solution,  as  in 
Pavy's  modification.  The  end-point  difficulty  is  perhaps  best  met 
by  using  Ling's  indicator:  Dissolve  in  lo  c.c.  water  at  45°  i  -5  grammes 
ammonium  thiocyanate  and  i  gramme  ferrous  anmionium  sulphate; 
cool  immediately;  add  5  c.c.  strong  HCl  when  a  brownish-red  solu- 
tion is  obtained.  The  colour  is  got  rid  of  b\'  adding  a  small  quantity 
of  zinc  dust.  To  determine  the  end-point,  remove  a  drop  of  the 
reduced  copper  solution,  and  mix  it  with  a  drop  of  the  indicator  on 
a  white  surface;  when  a  red  coloration  ceases  to  appear,  the 
reduction  is  complete. 

Genuine  commercial  milk-sugar  crystallized  from  water  gives : 

Not  more  than  0-05  per  cent.  ash. 

Solubility  at  15°  C.  =7-0  grammes  per  100  c.c.  (with  an  increase  of 
0"i  gramme  per  100  c.c.  for  each  degree  of  increase  of  temperature). 

Fall  of  temperature,  0-5°  C. 

Birotation  ratio,  i-6. 

Amount  of  milk-sugar,  99-5  to  99-9  per  cent. 

Milk-sugars  are  adulterated  with  cane-sugar,  maltose,  dextrose, 
and  various  mineral  matters.  Cane-sugar  can  be  detected  by 
treating  a  solution  with  yeast  at  55°  C.  for  six  hours.  Milk-sugar 
is  unchanged  in  specific  rotatory  power,  whilst  the  addition  of  as 
little  as  I  per  cent,  cane-sugar  produces  a  marked  change.  Maltose 
is  detected  b}'  a  decrease  in  the  birotation  ratio;  dextrose  by  an 
increase  in  this  ratio  and  a  decrease  in  the  fall  of  temperature. 

Adulteration  of  Milk. — The  principal  adulterations  are  the  addi- 
tion of  water  and  the  abstraction  of  cream. 

The  estimation  of  the  water  added  is  made  from  the  solids  not 
fat,  as  these  solids,  in  different  samples,  do  not  depart  so  far  from 
the  mean  as  the  fat.     The  legal  limit  is  8-5  per  cent. 

Example. — A  milk  yields  3  per  cent,  of  fat  by  one  of  the  foregoing 
processes  of  estimation,  and  11  per  cent,  of  total  solids.  The  sohds 
not  fat  amount  to  11  —3  =8  per  cent. 

On  the  assumption,  therefore,  that  8-5  per  cent,  represents  100 
per  cent,  pure  milk,  8  per  cent,  will  represent  94-1  per  cent,  pure 
milk. 

(8-5  :  8  :  :  100  :  94-1). 

In  other  words,  5-9  per  cent,  of  water  has  been  added  to  this 
sample. 


MILK  173 

It  may  be  urged  that,  since  a  few  animals  produce  milk  con- 
taining less  than  3  per  cent,  of  fat  and  less  than  8-5  per  cent,  of 
solids  not  fat,  it  is  unfair  to  the  dairyman  to  enforce  these  figures 
as  legal  limits.  But  the  number  of  animals  in  a  herd  producing 
milk  below  these  standards  is  so  small  in  proportion  to  the  whole 
number,  that  the  mixed  milks  should  in  all  cases  not  only  reach 
but  surpass  the  standards. 

Cane-sugar,  starch,  dextrin,  and  other  bodies  have  been  added 
to  mask  the  addition  of  water  by  raising  the  solids  not  fat;  these 
may  be  detected  by  the  sweet  taste,  deficiency  in  total  nitrogen, 
and  by  the  ash.  Starch  is  denoted  by  the  blue  colour  formed  with 
iodine.  Common  salt  has  been  added,  and  is  detected  in  the  ash 
by  increase  of  CI.  Chalk,  carbonate  and  bicarbonate  of  soda, 
borax,  fluorides,  etc.,  may  be  found.  Of  these,  borax  and  boracic 
acid  are  used  as  preservatives.  The  employment  of  preservatives 
— bodies  such  as  boric  acid,  formalin,  etc. — that  prevent  the  growth 
of  micro-organisms  has  been  much  discussed.  Some  hold  that  it 
is  better  to  add  these  bodies  than  to  allow  the  milk  to  decompose; 
whilst  others  advocate  the  exclusion  of  all  such  reagents. 

There  does  not  appear  to  be  any  experimental  evidence  to  show 
that  small  quantities  of  preservatives  like  boric  acid  and  its  com- 
pounds exert  an  injurious  effect  upon  healthy  adults,  or  even  upon 
healthy  children;  but  in  the  case  of  weakly  infants  there  is  a  strong 
feeling  in  favour  of  excluding  all  such  bodies  from  their  food. 
Salicylic  acid  holds  a  somewhat  different  position.  In  quantities 
necessary  to  prevent  the  growth  of  micro-organisms  this  drug  is 
likely,  in  certain  cases,  to  produce  injurious  effects.  Besides,  it 
inhibits  the  action  of  the  digestive  en2;ymes  of  the  alimentary  tract. 
Its  use  as  a  preservative  has  been  rightly  forbidden  in  France. 
Formalin,  formal,  or  formol  is  a  40  per  cent,  solution  of  formal- 
dehyde in  water,  and  in  the  strength  of  i  per  cent,  has  been  much 
used  as  a  milk  preservative.  It  produces  a  very  decided  change  in 
casein,  rendering  it  insoluble  in  the  digestive  juices.  A  patented 
process  exists  in  Germany  for  converting  casein,'  by  the  action  of 
formalin,  into  a  substance  resembling  celluloid.  This  preservative 
should  be  rigorously  excluded  from  all  foodstuffs.  The  question 
of  the  addition  of  preservatives  to  milk  has  another  aspect.  All 
purchasers  of  milk  expect  to  get  a  thoroughly  fresh  article.     Any 


174  PRACTICAL  SAXITARY  SCIEXCE 

procedure  allowed  the  dairyman  by  which  he  can  retain  milk  for 
a  number  of  days  puts  a  premium  on  the  sale  of  a  stale  substance. 
Milk  should  be  consumed  on  the  day  on  which  it  is  drawn  from  the 
animal.  Its  constitution  is  such  that,  apart  from  sterilization, 
which  can  only  be  legitimately  performed  by  heat,  it  rapidly  decom- 
poses and  becomes  unfit  for  consumption.  If  dairymen  were  com- 
pelled to  keep  their  churns  scrupulously  clean,  and  the  temperature 
of  the  milk  during  transit  sufficiently  low,  there  would  be  no  need 
for  preservatives,  and  we  should  hear  little  of  decomposed  milk. 

It  is  stated  that  a  mixture  of  boric  acid  and  borax  is  more  effica- 
cious in  preserving  milk  than  either  alone,  and  that  35  grains  of 
this  mixture  are  required  to  preserve  a  gallon  of  milk. 

Detection  of  Boric  Acid  or  Borax — The  Turmeric  Test. — Evap- 
orate 100  c.c.  of  the  milk,  which  has  been  made  alkaline  with  caustic 
soda  (0-5  gramme),  to  dryness;  incinerate.  Take  up  a  portion  of 
the  ash  in  water,  arid  the  remainder  in  weak  HCl.  Add  to  each 
portion  a  few  drops  of  freshly  prepared  turmeric  solution,  and 
evaporate  to  dryness.  When  boric  acid  or  borax  is  present,  the 
residue  assmnes  a  brownish-pink  colour,  which  changes  to  dark 
green  on  the  addition  of  a  solution  of  sodium  bicarbonate.  If 
the  watery  extract  gives  no  reaction,  whilst  the  acid  extract  reacts 
strongly,  it  may  be  concluded  that  borax  is  present;  if  the  two 
reactions  are  of  equal  intensity,  boric  acid  has  been  added;  and 
if  the  reaction  produced  b}'  the  acid  extract  is  stronger  than  that 
produced  by  the  watery  extract,  it  is  probable  that  a  mixture  of 
the  two  is  present. 

If  the  ash  be  moistened  with  dilute  H2SO4,  methylated  spirit 
added,  and  the  mixture  thorough^  stirred  and  set  on  lire,  a  green 
border  will  appear  on  the  flame  when  boric  acid  is  present. 

Estimation  of  Boric  Acid. — The  following  method  is  recom- 
mended by  R.  T.  Thompson:  To  100  c.c.  milk  add  2  grammes 
caustic  soda  and  evaporate  to  dryness  in  a  platinum  dish.  Char 
the  residue  thoroughly,  and  heat  with  20  c.c.  water.  Add  HCl  drop 
by  drop  till  all  but  carbon  is  dissolved.  Transfer  to  a  100  c.c. 
flask,  and  add  0"5  gramme  dry  CaClo-  Run  in  a  few  drops  of 
phenolphthalein,  and  then  a  10  per  cent,  solution  of  caustic  soda 
till  a  permanent  pink  colour  is  perceptible,  and  finally  25  c.c.  lime- 
water.     The  phosphoric  acid  is  all  precipitated  as  calcium  phos- 


MILK  175 

phate.  Make  up  to  100  c.c,  mix,  and  filter  througli  a  dry  filter. 
To  50  c.c.  of  the  filtrate  (representing  50  c.c.  of  the  milk)  add 
normal  sulphuric  acid  till  the  pink  colour  is  gone,  then  a  few  drops 
of  methyl  orange,  and  continue  the  addition  of  acid  until  the 
yellow  is  just  changed  to  pink.  Next  add  ^  NaOH  till  the  liquid 
assumes  a  yellow  tinge,  avoiding  excess  of  soda.  All  acids  likely 
to  be  present  at  this  stage  exist  as  salts  neutral  to  phenolphthalein, 
except  boric  acid,  which  is  neutral  to  methyl  orange,  and  a  little 
carbonic  acid,  which  latter  is  expelled  by  a  few  minutes'  boiling. 
Cool  the  solution,  add  a  little  more  phenolphthalein,  and  as  much 
glycerine  as  will  form  30  per  cent,  of  the  solution,  and  titrate  with 
^  NaOH  till  a  permanent  pink  is  produced.  Each  c.c.  of  ~  NaOH 
is  equal  to  0*0124  gramme  crystallizied  boric  acid  (  =0*007  gramme 
boric  anhydride). 

Phosphoric  acid  can  be  separated  from  boric  acid  by  precipitation 
as  calcium  phosphate,  if  not  more  than  0-2  per  cent,  of  crystalhzed 
boric  acid  be  present. 

It  is  necessary  not  to  carry  the  charring  further  than  that  required 
to  produce  a  colourless  solution,  as  excessive  heating  drives  oft 
boric  acid. 

Richmond  and  Miller  have  published  a  process  for  estimating 
boric  acid  without  ashing  the  milk  or  removing  phosphoric  acid: 
Weigh  about  10  c.c.  of  the  milk;  add  half  the  bulk  of  a  half  per  cent, 
phenolphthalein  solution;  run  in  normal  NaOH  till  pink  colour 
appears;  boil  and  titrate  back  with  normal  HCl  till  white,  and 
finally  with  ~r  NaOH,  till  faintly  pink  (colour,  though  faint,  is 
distinct) ;  add  30  per  cent,  of  glycerol  and  continue  the  titration  with 
^  NaOH.     [A  glycerol  blank  is  done  and  subtracted  if  necessary]. 

The  number  of  c.c.  y^  NaOH  used  for  the  final  titration,  multiphed 
by  0-0062,  gives  the  quantity  of  boric  acid  contained  in  the  quantity 
of  milk  operated  upon. 

Fopmalin.- — Pure  H2SO4  and  pure  formaldehyde  give  no  colour 
reaction  with  proteins.  Addition  of  small  quantities  of  oxidizing 
substances  such  as  hydrogen  peroxide,  ferric  chloride,  sodium 
peroxide,  potassium  persulphate,  etc.,  produces  a  characteristic 
colour.  The  reaction  fails  if  the  quantity  of  formaldehyde  is  in- 
creased beyond  a  certain  limit  which  is  in  proportion  to  the  amount  of 
oxidizing  reagent  used.  Rosenheim  has  shown  that  the  formaldehyde 


176  PRACTICAL  SAXITARY  SCIENCE 

is  oxidized,  producing  an  intermediate  oxidation  product,  wliich 
then  reacts  with  the  protein.  He  found  that  the  ammonium  com- 
pound of  diformaldehyde-peroxide-hydrate,  OH.CHoO.O.CH.O.OH, 
an  oxidation  product  intemiediate  between  formaldeh3-de  and  formic 
acid,  reacts  with  proteins  and  pure  sulpliuric  acid,  producing  the 
characteristic  colour.  This  is  a  general  reaction  for  proteins, 
and  depends  on  the  presence  of  tryptophane  (indol-amino-propionic 
acid).  The  intensity  of  the  reaction  with  different  proteins  varies 
directly  as  the  amount  of  tryptophane  present  in  the  protein  mole- 
cule, and  bodies  destitute  of  tryptophane  fail  to  give  the  reaction. 

Hehner's  Test. — To  10  c.c.  of  milk  in  a  test-tube  add  i  drop 
ferric  chloride  solution,  and  dilute  the  milk  to  about  30  c.c.  To  a 
portion  of  tliis  in  another  test-tube  add  concentrated  H2SO4,  by 
cautiously  pouring  it  down  the  side  of  the  tube  so  as  to  form  a 
laj'er  at  the  bottom  of  the  milk.  A  violet-blue  ring  will  be  formed 
at  the  junction  of  the  liquids. 

A  few  c.c.  of  the  milk  are  curdled  by  dilute  sulphuric  acid,  and 
a  little  Schiff' s  reagent  (a  solution  of  fuchsin  decolourized  by  sul- 
phurous acid)  added  to  the  filtrate  in  a  test-tube,  which  is  corked 
and  allowed  to  stand.  In  a  short  time  a  violet-pink  colour  is 
produced  in  the  presence  of  the  aldehyde. 

A  further  qualitative  test:  Boil  10  c.c.  of  milk;  add  a  few  drops 
25  per  cent.  HoSO,, ;  filter;  to  filtrate  add  5  c.c.  o-i  per  cent,  solution 
of  phloroglucin  and  5  c.c.  5  per  cent.  NaOH.  A  rose-pink  colour 
indicates  formalin. 

Estimation  of  Formalin. — There  is  no  satisfactory  method  of 
estimating  formalin.  An  approximate  estimation,  which  must  be 
made  early,  as  the  aldehyde  rapidh'  disappears,  may  be  carried  out 
by  the  following  method: — Reagents  required  :  a  normal  solution 
of  H2SO4,  a  few  100  c.c.  bottles,  with  close-fitting  rubber  stoppers, 
and  a  boiler,  in  which  they  may  be  immersed  to  the  neck,  a  solution 
of  methyl  orange,  and  an  approximately  normal  solution  of 
ammonia.  Place  in  each  bottle  25  c.c.  of  the  ammonia  solution, 
and  to  half  of  them  add  a  sample  containing  0-5  gramme  formalde- 
hyde. Stopper  tightly,  place  the  bottles  in  the  boiler,  fill  with 
water  to  the  neck,  and  boil  for  one  hour.  Cool  slowly,  and  titrate 
with  the  sulphuric  acid,  using  methyl  orange  as  indicator.  The 
differences  in  the  readings  of  the  blanks  and  the  samples  represent 


MILK  177 

the  ammonia  consumed  in  normal  c.c.  Each  c.c.  =  o-o6oi  gramme 
formaldehyde.  Any  acid  that  may  be  present  must  be  accounted 
for. 

The  following  method  originally  described  by  Shrewsbury  and 
Knapp  is  perhaps  as  satisfactory  as  any  other:  An  oxidiajing  reagent 
is  prepared  by  adding  0-05  to  o-i  c.c.  pure  HNO3  to  100  c.c.  con- 
centrated HCl.  Add  to  5  c.c.  of  milk  in  a  test-tube  10  c.c,  of  the 
reagent ;  shake  vigorously,  and  place  in  a  water-bath  at  a  tempera- 
ture of  50°  C.  In  about  ten  minutes  the  contents  of  the  tube  are 
cooled  to  room  temperature.  A  violet  colour  indicates  formalde- 
hyde, and  its  intensity  indicates  the  amount. 

The  quantitative  estimation  is  effected  by  setting  half  a  dozen 
milk  tubes  containing  known  quantities  of  formalin  at  the  same 
time  as  the  sample,  and  at  the  end  of  the  time  allowed  for  the  test 
selecting  the  match. 

Salicylic  Acid. — Precipitate  the  proteins  from  50  to  100  c.c. 
of  milk  by  the  addition  of  mercuric  nitrate,  and  filter.  Shake  up 
the  filtrate  with  half  its  volume  of  a  mixture  of  equal  parts  ether 
and  petroleum  ether,  and  stand  aside  until  the  ether  separates  out. 
Pipette  off  the  ether,  and  evaporate  to  dryness  in  a  clean  flask. 
Dissolve  th,e  residue  in  a  few  drops  of  hot  water,  and  add  to  a 
portion  of  the  solution  a  drop  of  a  i  per  cent,  ferric  chloride  solution  ; 
in  the  presence  of  salicylic  acid  a  violet  or  purple  colour  is  produced. 
Add  to  a  second  portion  of  the  solution  a  little  bromine  water: 
salicylic  acid  produces  a  curdy,  yellowish  precipitate.  Evaporate 
the  third  portion  of  the  solution  to  dryness  with  strong  HNO3, 
and  take  up  the  residue  in  a  few  drops  of  water.  If  salicylic  acid 
be  present,  a  yellow  coloration  is  produced  on  adding  ammonia. 

It  should  be  borne  in  mind  that  carbolic  acid  and  other  hydroxy- 
benzene  derivatives  act  in  a  somewhat  similar  manner  to  salicylic 
acid.  The  colour  reaction  with  ferric  chloride  remains  in  the  presence 
of  alcohol  in  the  case  of  salicylic  acid,  but  disappears  on  addition  of 
alcohol  in  the  case  of  carbolic  acid. 

A  further  test  consists  in  evaporating  a  part  of  the  ethereal 
extract  to  dryness,  placing  a  minute  portion  of  the  residue  in  the 
subliming  cell,  and  comparing  the  crystalline  subHmate  with  one 
obtained  from  pure  salicyl,ic  acid.  The  melting-point  of  pure 
salicylic  acid  is  155"^  to  156°  C. 

12 


ijS  PRACTICAL  SANITARY  SCIENCE 

A  quantitative  estimation  may  be  approximately  made  by 
matching  the  colour  produced  by  ferric  cliloride  in  a  standard  solu- 
tion containing  0-05  per  cent,  salicylic  acid  in  50  per  cent,  alcohol. 
A  I  per  cent,  iron  alum  is  recommended  instead  of  ferric  chloride. 
Definite  amounts  of  the  salicylic  acid  solution  should  be  added 
to  a  milk  filtrate  resembling  as  nearly  as  possible  that  of  the 
sample. 

Benzoic  Acid  is  but  very  occasionally  found  in  milk.  It  is  detected 
as  follows:  Render  alkaline  with  bar\i;a-water  200  c.c.  milk,  and 
evaporate  down  to  one-fourth.  Mi.x  the  residue  with  CaSO^  to 
form  a  paste,  and  dry  on  the  water-bath.  Powder,  moisten  with 
dilute  H0SO4,  and  extract  with  cold  50  per  cent,  alcohol.  Neutralize 
the  alcoholic  extract  with  baryta-water,  evaporate  to  small  volume, 
acidulate  with  dilute  H.jSOj,  and  extract  with  ether.  On  e\'aporating 
the  ether,  any  benzoic  acid  will  be  found  sufficienth'  pure  for  testing. 
Make  a  water^^  solution  of  the  benzoic  acid,  and  add  a  little  sodium 
acetate;  now  add  a  drop  or  two  of  ferric  cliloride  to  obtain  a  reddish- 
yellow  colour. 

HydPOg'en  Peroxide. — HgOo  in  the  presence  of  organic  matter 
rapidly  splits  into  water  and  oxygen.  If  milk  to  which  it  has  been 
added  be  examined  before  it  disappears,  it  may  be  detected  by 
addition  of  paraphen3dene-diamine,  when  a  blue  colour  is  produced. 
The  reaction  depends  on  the  presence  of  an  oxidase,  which  is 
destroyed  by  heat;  hence  if  the  sample  has  been  heated,  it  \x\\\ 
be  necessary  to  add  a  little  fresh  milk.  Milk  free  from  HaO,  de- 
colourizes Schardinger's  reagent  (5  c.c.  alcohoHc  methylene  blue, 
5  c.c.  formaldehyde,  190  c.c.  HgO),  but  milk  that  has  been  treated 
with  H2O2  ('  Buddeized  ')  fails  to  decolourize  the  reagent,  and  only 
regains  this  power  after  bacterial  fermentation  has  taken  place. 

Sodium  Carbonate. — Ash  a  weighed  portion  of  the  milk.  The 
ash  of  5  grammes  nomial  milk  does  not  contain  more  alkalinity 
than  that  neutralized  by  three-tenths  of  a  c.c.  of  j"^^  HCl.  Excess 
of  alkalinity  over  this  may  be  regarded  as  sodium  carbonate. 

Mix  10  c.c.  of  milk  with  10  c.c.  of  rectified  spirit  in  a  test-tube; 
add  2  or  3  drops  rosolic  acid  solution  (rosolic  acid,  i  gramme; 
alcohol,  25  c.c;  water  to  a  litre).  A  rose-pink  colour  indicates 
sodium  carbonate. 

A  preservative  named  '  mystin  '  (a  mixture  of  formaldehyde  and 


mii:k  -ijcj 

sodium  nitrite)  has  been  found  in  milk.  This  mixture  may  bo 
detected  by  destroying  the  nitrite  in  lo  c.c.  of  milk,  with  a  few  c.c. 
of  a  2  per  cent,  solution  of  urea,  and  then  testing  for  formaldehyde; 
or  by  distilling  off  the  formaldehyde  and  applying  Griess's  test  for 
nitrites. 

Colouping"  Matters. — The  most  commonly  occurring  colouring 
matter  is  the  vegetable  substance  annatto;  carrot  juice,  turmeric, 
and  saffron  are  also  used.  These  colouring  matters  are  all  soluble 
in  alcohol,  but  not  soluble  in  water. 

To  detect  annatto,  add  to  a  few  c.c.  of  milk  a  little  bicarbonate 
of  soda,  and  immerse  a  strip  of  white  filter-paper  over  night;  a 
brown  stain  in  the  paper  indicates  this  substance. 

If  an  alcoholic  solution  of  annatto,  saffron,  and  turmeric  be 
evaporated  down  to  dryness,  and  a  drop  of  concentrated  H2SO4 
placed  on  the  residue,  a  dark  blue  colour  is  produced,  changing  to 
green  in  presence  of  annatto  and  saffron.  In  the  case  of  saffron 
a  final  reddish-brown  is  formed.  Turmeric  produces  a  violet-red 
turning  brown  on  the  addition  of  an  alkali. 

Whilst  vegetable  colouring  matters  may  be  regarded  as  incapable 
of  damaging  the  digestive  organs  of  man,  it  is  not  clear  that  certain 
coal-tar  dyes  are  equally  innocent.  A  dilute  mineral  acid  added  to 
milk  containing  an  azio-coal-tar  dye  gives  a  pink  colour. 

Soup  Milk. — During  the  lactic  fermentation  of  milk  wherein  half 
the  lactose  may  be  transformed  into  lactic  acid  and  volatile  bodies, 
little  or  no  change  takes  place  in  the  fats.  But  before  estimating 
these  some  preliminary  treatment  of  the  curdled  sample  is  necessary. 
A  uniform  emulsion  is  made  by  means  of  a  whisk.  The  total  solids 
are  estimated  on  a  portion  of  this  in  the  usual  way. 

Fat  and  Non-Fat  Solids. — Weigh  10  grammes  into  a  flat  tared 
platinum  basin,  carrying  a  glass  rod;  add  2  drops  (0-5  per  cent.) 
phenolphthalein ;  run  in  decinormal  strontia  until  alkaline,  noting 
the  number  of  c.c.  used;  evaporate  on  a  water-bath  till  the  consis- 
tency of  dry  cheese  is  reached.  Pour  20  c.c.  of  dr}^  ether  over  the 
solids  and  thoroughly  triturate  with  the  glass  rod.  Decant  through 
a  dry  weighed  filter-paper  into  a  weighing  flask.  Repeat  the  ether 
treatment  several  times.  Distil  off  ether;  dry  and  weigh  residual 
iat. 

Transfer  the  solids  completely  to  a  weighing  flask ;  add  the  filter- 


i8o  PRACTICAL  SAX  IT  A  RY  SCIENCE 

paper  which  was  previously  thoroughly  washed  with  ether;  dry 
for  three  hours  at  loo^,  and  weigh;  dry  for  a  further  two  hours 
and  again  weigh;  drj-  for  another  liour  and  weigh  (last  two  weights 
should  not  differ  by  more  than  a  milligramme).  Deduct  0-00428 
gramme  for  each  c.c.  of  strontia  used,  also  the  weight  of  the  filter- 
paper.     Result  =non-fat  solids. 

Correction  for  Alcohol  formed  from  Lactose. — Distil  100 
grammes  of  the  milk  and  neutralize  the  distillate  with  -j^g-  XaOH 
(litmus  indicator).  Redistil  the  neutralized  distillate  and  calculate 
the  percentage  amount  of  alcohol  from  an  alcohol  table.  The 
percentage  weight  of  alcohol,  x  4'"  =  percentage  of  lactose  that  has 
disappeared  in  formation  of  alcohol. 

Correction  for  Volatile  Acids. — Determine  the  total  acidity  in 
10  grammes  of  the  milk  by  y^y  XaOH  (phenolphthalein  indicator). 
Weigh  another  10  grammes  of  the  sample  in  a  platinum  dish,  and 
add  half  the  quantity  of  y^^  XaOH  necessary  to  neutralize.  Evapor- 
ate to  dr}-ness  on  a  water-bath  with  frequent  stirring;  add  20  c.c. 
boiling  water  and  thoroughly  detach  solids  from  dish;  now  add 
j""^  XaOH  till  neutral.  Difference  between  original  acidity  and 
acidity  of  evaporated  portion  =  volatile  acidity  recorded  as  acetic 
acid;  and  60  parts  acetic  acid  (CH3COOH)  =62  parts  original  lactose 
(CO.2-1-H2O).  Richmond  rightly  points  out  that  this  correction 
is  inaccurate — COo  driven  off  is  calculated  as  acetic  acid;  all  volatile 
acids  are  not  driven  off ;  there  is  a  possibility  of  lactic  acid  being 
volatile,  and  it  may  be  converted  into  a  lactose. 

Thorpe  makes  an  ammonia  correction:  2  grammes  of  milk  are 
made  up  to  100  c.c.  with  ammonia-free  distilled  water,  and  filtered 
through  a  carefully  washed  filter.  Ten  c.c.  of  the  clear  filtrate  are 
similarly  made  up  to  50  c.c.  in  a  Xessler  glass,  and  the  ammonia 
estimated  bv  standard  ammonium  chloride  (i  c.c.  =o-oi  milligramme 
XH3)  after  Xessler's  method. 

Richmond  shows  good  reasons  for  regarding  the  ammonia  correc- 
tion as  unnecessar}'. 

The  total  correction  (0-2  to  0-3  per  cent,  additive)  is  fairly  con- 
stant in  properly  sealed  samples  three  to  six  weeks  old. 

Bacteria  in  Milk. — Micro-organisms  enter  milk  from  the  udder, 
during  milking,  and  during  transit  and  distribution.  It  is  not 
possible  to  estimate  the  total  number  of  bacteria  in  milk.     Perhaps 


MILK  i8i 

the  best  count  is  that  which  demonstrates  the  presence  of  pollution 
by  manure:  B.  colt,  B.  enteritidis  sporogenes. 

The  methods  employed  in  this  work  differ  in  no  main  principle 
from  those  used  in  connection  with  water.  The  utmost  care  is 
necessary  in  the  collection  of  samples.  Dilutions  are  conveniently 
made  in  sterile  flasks  or  bottles  by  placing  lO  c.c.  of  milk  or  of  a 
particular  dilution  in  the  vessel  which  already  contains  90  c.c.  of 
sterile  distilled  water. 

Estimation  of  B.  Coli. — To  a  series  (better  to  a  double  series)  of 
lactose,  bile-salt  broth  tubes  are  added  respectively — i-o,  o-i,  o-oi, 
o-QOi,  o-oooi,  o-ooooi,  o-oooooi  c.c.  (and  smaller  fractions,  if  neces- 
sary, depending  on  the  degree  of  pollution  of  the  sample.)  Record 
is  made  of  the  smallest  quantity  producing  acid  and  gas  in  two  days 
at  37°  C. 

B.  Enteritidis  Sporogenes. — Add  i,  1-5,  and  2  c.c.  of  the  sample 
to  tubes  containing  10  c.c.  fresh  milk  recently  sterilized.  Add 
5,  10,  and  20  c.c.  to  empty  sterile  tubes.  Heat  the  six  tubes  for 
ten  minutes  at  80°  C.  Cool  promptly  and  incubate  anaerobically 
for  two  days  at  37°  C.  Look  for  the  characteristic  enteritidis 
changes. 

Pathogenic  Micro-Organisms  —  B.  Tuberculosis.  —  Centrifugalize 
50  or  100  c.c.  of  the  milk.  Examine  a  portion  of  the  sediment 
microscopically.  Make  and  fix  films  on  microscopic  slides.  When 
thoroughly  fixed,  wash  out  all  fat  with  a  mixture  of  equal  parts 
of  anhydrous  ether  and  absolute  alcohol.  Stain  by  the  Ziehl- 
Neelsen  method.  Use  the  remainder  of  the  sediment  for  inoculating 
several  guinea-pigs  subcutaneously  on  the  inner  side  of  the  left 
leg.  Evidence  of  infection  may  be  found  at  various  subsequent 
dates  in  enlargement  of  the  popliteal,  inguinal,  sublumbar,  and 
retro-hepatic  lymph  glands  on  left  side,  and  in  tubercles  in  the 
spleen.  Four  weeks  is  an  average  time  for  the  production  of  these 
appearances.  When  the  milk  contains  large  number  of  B.  tuber- 
culosis, they  may  be  found  as  early  as  fifteen  days  after  inoculation ; 
when  few  bacilli  exist,  five  to  six  weeks  may  be  required  to  give 
results.  It  is  well  to  make  smears  from  the  enlarged  glands  and 
stain  with  Ziehl-Neelsen's  fluid.  Inasmuch  as  certain  non-patho- 
genic acid-fast  bacteria  presenting  morphological  characters 
somewhat  similar  to   B.   tuberculosis- — such   as  Moller's  Timothy- 


iS2  PRACTICAL  SANITARY  SCIENCE 

grass  bacilli,  Rabinowitcli's  butter  bacillus,  the  smegma  bacillus, 
mist  baziUns,  and  Johne's  bacillus — produce  tubercular  lesions  in 
the  guinea-pig  somewhat  resembling  those  produced  by  B.  tubercu- 
losis, it  is  not  always  safe  to  rely  on  inoculation.  The  diagnosis 
can  be  established  definitely  bj^  sowing  on  glycerin,  agar,  or  other 
media  portions  of  the  pulp  of  the  lymph  glands,  from  which  the 
smears  above  mentioned  are  made.  All  the  non-pathogenic 
organisms  will  form  definite  growths  in  two  or  three  days,  whereas 
B.  tuberciUosis  will  ordinarily  require  three  or  four  weeks  for  growth. 
It  is  necessary  to  investigate  the  cream  in  all  these  details,  as  well 
as  the  sediment. 

The  Klebs-Loffler  Bacillus. — Sediment  and  cream  arc  investigated 
morphologically  and  culturally.  If  organisms  resembling  the  diph- 
theria bacillus  morphologically  are  found,  they  must  be  growm  on 
blood  serum,  and  their  virulence  must  be  tested  by  animal  inocula- 
tion. 

B.  Typhosus. — This  organism  is  almost  as  difficult  to  detect  in 
milk  as  in  water.  Portions  of  sediment  and  cream  are  applied  to 
those  media  intended  for  the  differentiation  of  B.  typhosus,  such  as 
lactose  bile  salt  neutral  red  agar,  followed  by  subculture  on  Conradi 
and  Drigalski's  medium,  malachite  green  agar,  etc. 

Streptococci. — In  the  milk  of  cow^s  suffering  from  mastitis, 
enormous  numbers  of  streptococci  are  found,  and  when  these  are 
inoculated  into  the  teats  of  goats,  they  set  up  an  inflammatory 
reaction.  But  since  they  are  found  in  certain  numbers  in  the 
milk  oi  healthy  cows  collected  in  the  most  cleanly  manner,  it  is 
difficult,  if  not  impossible,  to  estimate  their  significance.  All 
that  can  be  said  at  the  moment  is,  that  where  streptococci 
exist  in  milk  in  large  numbers,  the  indication  is  to  examine  the 
animal  for  mastitis,  ulceration  of  teats,  etc.  Streptococci  arise 
from  the  teats  and  milk  ducts  of  the  udder,  in  large  quantities  from 
manure,  in  smaller  quantities  from  the  air,  and  may  be  contributed 
by  filthy  vessels,  foul  water,  etc. ;  and  in  those  cases  where  they 
occur  in  very  large  numbers,  if  no  inflammatory  condition  of  the 
udder  be  found,  it  may  be  assumed  that  their  presence  is  most  likely 
due  to  manure.  They  can  be  readily  demonstrated  in  the  sediment 
b}'  making  smears  and  staining  with  methylene  blue. 

Quantitative  estimation  is  effected  by  inoculating  glucose  neutral 


MILK  183 

red  broth  with  i-o,  o-r,  o-oi,  o-ooi  c.c,  etc.,  Jind  incuijiitin/^  for  two 
days  at  37^  C.  Hanging-drop  ;i,nd  stained  ]:)re])arations  exliihit 
definite  chains  of  cocci. 

Cellular  Elements  of  Milk.^ — These  are  recovered  and  studied 
in  the  sediment  microscopically.  Where  pus  enters  milk  in  large 
quantities,  the  fact  is  at  once  revealed  by  a  microscopic  examina- 
tion. But  whether  a  few  round  cells  resembling  dead  leucocytes 
are  to  be  regarded  as  evidence  of  a  small  quantity  of  added  pus 
or  as  normal  constituents  of  certain  milk  remains  an  open 
question. 

Bacteriological  examination  of  condensed  milk,  dried  milk,  and 
cheese  is  carried  out  in  the  same  manner  after  a  thorough  emulsion 
has  been  made  of  a  definite  weight  of  the  substance  in  sterile  water. 

Koumis. — The  original  koumis  was  made  by  the  Tartars  from 
mares'  milk,  which  is  rich  in  lactose,  and  readily  fermented.  This 
stimulating,  beverage  is  now  largely  made  from  cow's  milk,  to  which 
sugar  and  yeast  have  been  added.  It  undergoes  a  multiple  fermen- 
tation— alcoholic,  lactic,  and  proteolytic. 

Kephir. — This  is  a  fermented  milk  similar  to  koumis.  The 
proteolytic  fermentation  is  less  pronounced,  and  the  alcoholic  and 
latic  fermentations  are  established  by  a  fungus — kephir  grains. 

Condensed  Milks  are  found  in  four  forms:  (i)  Condensed  whole 
milk  sweetened;  (2)  condensed  whole  milk  unsweetened;  (3)  con- 
densed separated  milk  sweetened;  (4)  condensed  separated  milk 
unsweetened.  The  process  of  condensing  unsweetened  milk  appears 
to  kill  all  bacteria,  and  organisms  that  are  found  in  this  variety, 
according  to  Gordon,  are  introduced  subsequently  from  the  air. 
In  all  the  sweetened  varieties  streptococci,  with  characters  similar 
to  those  found  in  milk,  were  discovered  by  the  same  observer. 

The  chemical  and  bacteriological  examinations  of  these  modifica- 
tions of  milk  are  worked  out  on  the  same  lines,  as  in  the  case  of 
ordinary  milk,  condensed  milks  being  first  mixed  with  a  definite 
measured  quantity  of  distilled  water. 

Dried  or  powdered  milk  is  produced  (i)  by  applying  the  fluid  in 
a  thin  stream  to  the  surface  of  a  heated  revolving  metallic  cylinder, 
or  (2)  by  passing  it  in  the  form  of  a  fine  spray  into  a  hot-air  chamber. 
It  should  contain  fully  27  per  cent,  of  fat,  and  about  32  per  cent, 
each  of  proteins  and  sugar. 


1 84  PRACTICAL  SAXITARY  SCIENCE 

The  fat  is  best  estimated  by  Adam's  process,  and  the  proteins  by 
Kjeldahl's  total  organic  nitrogen  process,  using  the  factor  6-38. 

Cream  is  prepared  by  centrifugalizing  milk,  and  contains  45  to 
63  per  cent,  of  fat.  Cream  is  artilicially  thickened  with  gelatin, 
starch  paste,  condensed  milk,  and  saccharate  of  lime.  Gelatin 
mav  be  detected  by  drying  a  weighed  quantity  and  washing  out 
the  fat  with  ether.  The  residue,  when  dissolved  in  boihng  water, 
will  contain  the  gelatin,  which  sets  on  cooling.  Or  mix  a  weighed 
quantity  of  cream  with  warm  water:  precipitate  proteins  and  fat 
with  acetic  acid;  filter;  add  to  the  clear  filtrate  a  little  strong  solu- 
tion of  tannin,  when,  if  gelatin  be  present,  a  voluminous  precipitate 
falls  out.  A  control  sample  of  genuine  cream  should  be  operated 
on  in  the  same  way.     It  will  give  but  a  shght  precipitate. 

Starch  is  discovered  by  the  blue  colour  it  forms  with  a  solution 
of  iodine. 

Calcium  saccharate  is  determined  as  CaO  in  the  ash.  The 
dicalcium  phosphate,  tricalcium  phosphate,  calcium  citrate,  and 
lime  united  with  proteins  in  normal  cream,  when  transformed  into 
CaO,  amount  to  about  22-5  per  cent,  of  the  ash. 

Cane-sugar  in  cream  is  detected  by  the  rich  red  colour  produced 
when  to  15  c.c.  of  cream,  O'l  gramme  of  resorcinol,  and  i  c.c.  of  con- 
centrated HCl  are  added,  and  the  mixture  raised  to  the  boiling- 
point. 

BUTTER. 

Butter  is  produced  from  milk  or  cream  by  churning.  The  agita- 
tion causes  the  fat  globules  to  coalesce  to  form  granules  of  a  fine 
spongy  nature.  When  butter  is  collected  and  worked,  it  assumes 
a  more  homogeneous  appearance. 

The  mean  composition  of  butter  made  from  ripened  cream,  accord- 
ing to  Storch,  is : 

Per  Cent. 

Fat  .  .  . .  . .  . .     82-97 


Water 

Proteins 

Milk-sugar 

Ash 

Salt 


1378 
0-84 

0-39 
o-i6 
1-86 


The  composition  of  different  butters  varies  considerably. 

If  butter  be  churned  at  a  higher  temperature  than  13°  to  18''  C.^ 


BUTTER  185 

it  will  contain  more  water  than  at  medium  temperatures.  Very 
low  temperatures  and  rapid  (duirninj,^  produce  an  article;  containing 
too  much  water. 

Butter  is  adulterated  with  various  foreign  fats,  animal  and  vege- 
table, under  the  name  of  margarine,  which  as  a  rule  are  little 
inferior  in  nutritive  qualities  to  the  fat  of  milk.  In  the  pro- 
duction of  margarine,  animal  and  vegetable  fats  are  melted,  filtered 
through  coarse  filters,  and  worked  up  with  milk,  to  look  and  smell 
like  pure  butter. 

It  is  stated  that  margarine,  as  prepared  for  the  market,  is  not 
quite  so  digestible  as  butter.  Whether  or  not  this  be  true,  it  is 
illegal  to  substitute  margarine  for  butter,  and  the  principal  object 
of  a  butter  analysis  is  to  determine  the  presence  or  absence  of 
foreign  fats. 

The  odour  and  taste  of  butter  are  characteristic,  and  excellent 
tests  of  its  purity.  By  heating  it  to  25°  C.  any  unpleasant  taste 
that  it  may  possess  becomes  more  apparent. 

Adulteration. — Foreign  fats  are  the  chief  item  of  adulteration. 
Colouring  matters,  especially  annatto,  are  employed.  Water  is 
worked  into  butter  for  the  purpose  of  increasing  its  weight;  but, 
as  the  addition  of  water  renders  butter  liable  to  decomposition,  it 
is  only  possible  to  escape  detection  in  cases  where  the  butter  is 
rapidly  disposed  of.  The  addition  of  pepsin,  rennet,  etc.,  -to  milk 
before  churning  aims  at  increasing  the  yield  of  butter  by  securing 
an  increase  of  contained  water. 

The  Estimation  of  Water. — At  present  butter  is  allowed  to 
contain  16  per  cent,  of  water.  The  following  two  methods  readily 
determine  the  amount  of  water;  the  second  is  the  more  accurate. 

1.  Weigh  out  10  grammes  of  butter  into  a  small  platinum  or 
porcelain  basin  provided  with  a  piece  of  glass  rod.  Heat  on  a  sand- 
bath  or  over  a  small  flame,  and  carefully  stir  until  all  frothing 
ceases.  It  is  necessary  to  regulate  the  temperature  so  that  the 
curd  is  not  appreciably  browned  during  the  heating,  and  that  there 
is  no  loss  by  spirting.  The  basin  with  its  contents  is  cooled  in  a 
desiccator  and  weighed.  The  loss  of  weight  represents  the  water 
in  10  grammes. 

2.  Fill  a  small  platinum  or  porcelain  basin  with  pieces  of  pumice 
that  have  been  recently  washed  and  ignited.  Select  portions  of 
butter  from  three  different  regions  of  the  sample  (water  is  not  always 


1 86 


PR  A  C  TIC  A  L  SA  XITA  R  \ '  SCIEXCE 


equally  distiilnitcd  thri)\iglu)ut  tlu'  mass  of  butter),  and  plaee  them 
in  a  clean,  wide-mouthed,  stoppered  bottU'.  Melt  at  as  low  a  tem- 
perature, as  possible,  and  shake  vigorously  until  the  mass  is  solid. 
Place  5  grammes  of  this  mass  in  the  porcelain  basin,  and  heat 
in  a  drying-oven  with  good  draught  at  ioo°  C.  for  an  hour.  Cool 
and  weigh.  Replace  in  the  oven  for  a  further  half-hour,  and  again 
cool  and  weigh.  Repeat  the  heating  and  weighing  until  a  constant 
weight  is  obtained.  The  difference  between  the  lowest  weighing 
and  that  of  the  original  butter  is  taken  as  water. 


r.eaker  for  melting     Bottle  beaker  with  funnel     Graduated  test-tube         Platinum 
crude  butter.  for  filtering  butter-fat.  for  Valenta  test.  basin. 

Fig.  28. 


The  following  table  represents  the  variations  of  water  in  Danish 
butters : 


Number  of  .Samoles. 

entage  of  Water.                                                      Summer.                    Winter. 

9  to  10 

I                                   I 

10    .,    II 

16                   8 

II     ,,     12 

136                 20 

12    ,,    13 

335                138 

13    „    14           .  . 

534                431 

14    ,,    15           .- 

512                562 

15    ,,    16 

287                447 

16    ,,    17 

124                205 

17    ,,    18 

39                 95 

18    ,,     19           .  . 

13                  20 

Above  19 

4                   3 

Average 

I 

4-03  per  cent.     14-41  per  cent 

BUTTER  187 

Butters  containing  13-5  per  cent,  of  water  are  said  to  liave  the 
best  flavour. 

Estimation  of  Curd  and  Salt.— The  residue  from  the  deter- 
mination of  water  is  taken  and  melted  at  a  low  temperature.  Ether 
is  added,  and  the  whole  well  stirred  and  set  in  a  warm  place  until 
the  ether  is  quite  clear,  when  the  fluid  is  decanted  into  a  small 
weighed  flask.  Fresh  ether  is  poured  on  the  residue,  and  when 
clear  poured  off.  This  treatment,  repeated  three  or  four  times, 
removes  the  whole  of  the  fat.  A  little  practice  and  ordinary  care 
will  prevent  any  of  the  non-fatty  solids  being  poured  away  with 
the  solvent.  The  residue  is  dried  in  the  hot-air  oven  to  constant 
weight,  and  represents  salt  and  solids  not  fat. 

The  Salt. — To  estimate  the  salt,  the  residue  from  the  last  deter- 
mination is  treated  with  hot  water  and  filtered.  The  filter  with 
its  contents  is  well  washed,  and  the  filtrate,  when  cold,  is  titrated 
with  standard  nitrate  of  silver,  using  a  5  per  cent,  solution  of 
neutral  potassium  chromate  as  indicator.  The  amount  of  sodium 
chloride  is  easily  calculated.  The  silver  nitrate  should  be  standard- 
ized on  pure  sodium  chloride. 

Curd. — ^The  estimation  of  the  proteins  is  best  effected  by 
Kjeldahl's  process  for  the  estimation  of  total  N  on  the  residue  left 
after  estimating  the  fat,  and  multiplying  the  N  by  6-38. 

The  Fat. — This  item  is  estimated  by  subtracting  the  combined 
weights  of  water,  salt,  and  solids  not  fat  from  100.  As  a  control 
the  ethereal  extract  may  be  evaporated,  and  the  fat  residue 
weighed. 

Preservatives. — Besides  salt,  several  substances  are  used  as 
preservatives,  such  as  boric  acid,  borax,  formalin,  salic^dates, 
sulphites,  and  nitrates.  These  are  all  estimated  in  the  watery 
fluid  which  separates  out  underneath  the  fat  on  heating  the  butter. 

The  estimation  of  boric  acid  is  carried  out  as  follows  :  Heat 
10  grammes  of  butter  in  a  dish;  wash  out  the  melted  mass  into  a 
separating  funnel  with  about  50  c.c.  boiling  water;  shake  thoroughly, 
and  when  fat  is  separated  run  off  the  water  into  a  100  c.c.  flask. 
Repeat  this  treatment  twice,  using  less  than  25  c.c.  boiling  water 
each  time.  When  all  the  washings  are  collected  in  the  flask  and 
cold,  make  up  to  the  100  c.c.  mark.  Filter  through  a  drj^  Alter, 
and  titrate  50  c.c.  as  described  on  p.  175.     The  titration  may  be 


iSS  PRACTICAL   SANITARY  SCIENCE 

perfomicd  on  this  solution  without  any  trcatnient.  as  butter  is  free 
from  phosphates. 

Formalin  cannot  be  estimated  with  any  degree  of  exactitude,  as 
it  enters  into  combination  with  the  proteins,  so  that  the  uncom- 
bined  formahn  alone  reacts,  and  this  gives  no  information  as  to  the 
amount  originally  added. 

To  estimate  salicylic  acid  treat  20  grammes  of  butter  with 
a  solution  of  sodium  bicarbonate  several  times  in  a  separating 
funnel :  salicylic  acid  is  converted  into  sodium  salicylate.  Acidify 
the  extract  with  dilute  H2SO4,  and  extract  with  ether;  evaporate  the 
ether,  and  to  the  residue  add  a  little  mercuric  nitrate,  forming  a 
precipitate  nearly  insoluble  in  water.  Filter  the  precipitate  off, 
and  wash  it  with  water.  From  the  washed  precipitate  liberate  free 
salic3'lic  acid  with  dilute  H.^SOj.  Redissolve  in  ether,  evaporate, 
and  dry  residue  at  100°  C.  Extract  the  residue  with  petroleum 
ether,  and  add  an  equal  volume  of  95  per  cent,  alcohol.  Titrate 
with  y^  KOH  (phenolphthalein  indicator),  [i  c.c.  ^^  KOH  = 
0-0138  gramme  salicylic  acid.]  Processes  which  depend  on  the 
precipitation  of  proteins  and  detection  of  preservatives  in  the 
filtered  liquid  are  liable  to  error  owing  to  the  great  solubility  of 
salicylic  acid  and  benzoic  acid  in  butter-fat.  The  extraction  of  the 
fat  with  solvents  (ether,  alcohol,  chloroform,  etc.)  frequently  gives 
rise  to  troublesome  emulsions.  To  overcome  these  troubles  Monicr- 
Williams  has  devised  a  method  of  detecting  small  quantities  of 
benzoic  acid,  saccharin,  and  salicylic  acid  in  cream :  Acidify 
100  grammes  of  cream  with  i  c.c.  concentrated  phosphoric  acid; 
heat  with  constant  stirring  either  in  a  porcelain  dish  on  gauze  over 
a  Bunsen  or  on  a  boiling-water  bath  in  vacuo  (temperature  should 
not  rise  above  120°  C.)  until  all  water  is  expelled.  At  least  95  per 
cent,  of  the  salicylic  and  benzoic  acids  remain  in  the  fat,  and  only 
the  merest  traces  escape  in  the  steam.  Filter  the  clear  fat  through 
a  dry  filter.  Allow  the  fat  to  cool  to  60''  to  70°  C;  shake  with 
50  c.c.  of  0-5  per  cent,  sodium  bicarbonate  previously  heated  to 
60°  to  70"  C;  when  separated  from  the  fat  filter  the  alkaline  liquid 
through  a  wet  filter;  acidify  with  i  c.c.  concentrated  HCl;  cool,  and 
extract  three  times  with  15  to  20  c.c.  ether.  Dry  combined  ether 
extract  with  CaClg,  and  distil  off  ether.  The  residue  will  have  a 
distinctly  sweet  taste  if  saccharin  be  present.     Stir  the  residue  on 


BUTTER  189 

a  water- bath  with  i  c.c.  strong  ammonia;  evaporate  to  dryness; 
add  three  or  four  drops  of  water  and  a  drop  of  10  per  cent,  iron  alum 
solution  on  a  glass  rod.  The  characteristic  purple  colour  appears  in 
presence  of  salicylic  acid,  and  a  buff-coloured  precipitate  in  the 
presence  of  benzoic  acid.  The  method  is  said  to  detect  with  cer- 
tainty in  100  grammes  of  cream  the  following  quantities  of  these 
preservatives  occurring  singly  or  all  together:  0-0075  per  cent, 
benzoic  acid;  o-ooi  per  cent,  saccharin;  0-0002  per  cent,  salicylic 
acid. 

Sulphites. — A  portion  of  the  watery  liquid  is  distilled  with 
dilute  HCl,  and  the  gas  evolved  is  passed  into  -^^^  I  solution,  which 
in  turn  is  titrated  with  sodium  thiosulphate.  Sixty-four  parts  of 
SO2  are  converted  into  sulphuric  acid  by  254  parts  of  I.  Or  the 
SO2  gas  may  be  passed  into  bromine-water,  and  the  H2SO4  formed, 
estimated  as  BaS04.  Sixty-four  parts  SOg  represent  233-5  parts 
BaS04. 

Butter-Fat:  Preparation  of  Fat  for  Analysis.— A  portion 
of  the  sample  of  butter  is  placed  in  a  beaker  and  heated  at  a  tem- 
perature of  45°  to  48°  C.  in  an  air-oven.  In  a  little  time  three 
layers  separate  out  in  the  beaker.  The  largest,  the  butter-fat, 
containing  a  few  particles  of  curd  in  suspension  and  a  few  drops 
of  water  underneath  the  surface  film  on  the  top;  a  greyish- white 
layer,  the  curd,  near  the  bottom ;  and  underneath  a  small  quantity 
of  water.  If  the  sample  be  genuine  butter,  the  melted  fat  is  quite 
transparent,  whereas  if  mixed  with  margarine,  melted,  and  re- 
emulsified,  churned  at  a  high  temperature,  or  rancid,  it  is  generally 
turbid. 

The  fat  is  poured  on  a  dry  filter  kept  at  a  temperature  above  the 
melting-point  of  butter,  and  is  now  free  from  the  other  constituents, 
except  about  o-i  per  cent,  of  water,  and  a  trace  of  lactic  acid.  These 
manipulations  are  readily  carried  out  by  placing  the  beaker  con- 
taining the  melted  butter,  and  a  second  beaker  (carrying  a  fiinnel 
and  filter-paper)  in  which  the  fat  is  received,  on  the  top  of  an  air- 
oven  whose  inner  temperature  approaches  but  does  not  exceed 
50°  C.  After  filtration  the  fat  is  rapidl}^  cooled  so  as  to  prevent 
partial  solidification,  and  to  obtain  a  homogeneous  mass. 

Butter-fat  contains  considerable  quantities  of  the  glycerides  of 
the    fatty-acid   series    CnHzn+iCOOH,    of    low    molecular    weight. 


i()o  PRACTICAL  SAXITARY  SCIEXCE 

The  lowest  and  most  important  is  butyric  acid.  Acids  of  the  oleic 
series  are  also  present. 

The  various  foreign  fats  which  are  admixed  with  butter,  such  as 
beef  and  mutton  fats,  lard,  cottonseed  oil,  and  other  vegetable 
oils,  present  several  important  physical  and  chemical  differ- 
ences. 

Physical  Properties  of  Fats  :  i .  Melting-Point. — Fats  arc 
not  single  substances,  but  mixtures  of  different  glycerides;  the 
melting-points  are  therefore  not  sharp.  The  melted  fat  is  drawn 
into  a  capillary  tube  i  millimetre  bore,  so  as  to  give  a  column  about 
I  centimetre  in  length.  Not  less  than  a  day  should  elapse  before  the 
test,  as  even  pure  glycerides  of  fatty  acids  that  are  single  chemical 
entities  melt  at  a  much  lower  temperature  if  they  have  been  recently 
melted  than  that  at  which  they  melt  if  they  are  kept  in  the  solid 
state  for  some  time.  The  capillar}'  is  attached  by  a  rubber  band 
to  the  stem  of  a  delicate  thermometer,  reading  tenths  of  a  degree,  so 
that  the  column  of  solidified  fat  is  opposite  the  thermometer  bulb. 
The  thermometer  and  its  attached  capillary  tube  are  then  immersed 
in  water  in  a  test-tube,  and  the  test-tube  in  turn  is  immersed  in  a 
beaker  of  water  mounted  on  gauze  over  a  Bunsen  burner.  The 
water  in  the  beaker  is  heated  gradually  (rise  of  temperature  not  to 
exceed  0-5°  C.  per  minute),  and  the  exact  temperature  noted  at 
which  fusion  of  the  fat  occurs:  this  is  the  melting-point.  The 
f\a.me  is  removed,  and  the  temperature  noted  at  which  the  fat 
solidifies:  this  is  the  solidifying-point.  Butter-fat  melts  at  about 
33°  C.  Some  foreign  fats  have  melting-points  lying  very  near  to 
that  of  butter-fat;  moreover,  artificial  butters  are  made  to  melt  at 
the  same  temperature  as  butter,  so  this  test  is  of  little  practical 
value  in  distinguishing  pm-e  butter  from  margarine. 

2.  Specific  Gravity.  —  On  account  of  the  glycerides  of  low 
molecular  weight  which  it  contains,  butter-fat  has  a  greater  density 
than  the  fats  used  to  adulterate  it.  As  it  is  more  convenient  to 
take  the  specific  gravity  of  a  fluid  than  a  solid,  and  as  Skalweit 
found  that  at,  or  around,  the  temperature  38°  C.  there  is  the  greatest 
difference  between  the  specific  gravities  of  butter  and  foreign  fats, 
this  temperature  is  usually  adopted  for  the  taking  of  specific 
gravities. 

Fill  the  pycnomcter  with  water  at  38°  C.  and  weigh  it.     Remove 


BUTTER  10  f 

the  water  and  dry  the  flask  in  an  air-oven  tliroiigli  whidi  a  j^ood 
current  of  air  passes.  Now  fill  it  with  fat,  and  place  it  in  water 
at  38°  C.  till  the  volume  is  constant.  Weigh  again  rapidly,  and 
the  weight  of  the  fat  divided  by  the  weight  of  water  gives  the 
specific  gravity  at  38°  C.  The  limits  of  specific  gravity  for  pure 
butter-fat  at  38°  C.  are  0-914  and  0-909.  The  fats  usually  added  as 
adulterants  have  a  mean  specific  gravity  of  0-903. 

The  density  may  also  be  determined  by  a  hydrometer  or  by  West- 
phal's  balance  at  38°  C. 

The  presence  of  glycerides  of  lower  fatty  acids  raises  the  specific 
gravity  of  a  fat;  hence  rancidity  is  accompanied  by  an  increase  in 
the  specific  gravity. 

A  pycnometer  with  capillary  side-tube  can  be  used  for  estimating 
the  specific  gravity  of  solid  fats :  the  bottle  is  filled  with  water  and 
weighed;  a  weighed  amount  of  the  solid  fat  is  introduced  and  the 
stopper  inserted.  The  diminution  of  weight  plus  the  weight  of  the 
solid  fat  gives  the  amount  of  water  displaced  and  the  volume  of 
the  fat. 

3.  Solidification-Point  and  litre  Test.— When  melted  fat  is 
cooled,  the  temperature  falls  gradually  to  a  variable  degree,  then 
rises  rapidly  to  a  certain  constant  temperature,  at  which  it  remains 
steady  for  a  time  before  it  begins  to  fall  again;  this  maintained 
temperature  is  the  solidification -point.  This  test  is  generally 
carried  out  on  the  fatty  acids  obtained  by  saponification  of  the  fats, 
and  is  then  known  as  the  '  Titre  test.'  A  method  of  carrying  it  out 
is  the  following:  Saponify  75  grammes  of  the  fat  in  a  metal  dish 
with  60  c.c.  of  30  per  cent.  NaOH  and  75  c.c.  95  per  cent,  alcohol, 
or  120  c.c.  water.  Evaporate  to  dryness  and  dissolve  in  i  litre  of 
water.  Boil  to  remove  alcohol.  Add  100  c.c.  30  per  cent.  HgSOj, 
and  heat  till  clear:  the  fatty  acids  are  separated.  Wash  them  with 
hot  water  till  free  from  soluble  acids,  and  filter  through  a  dry  filter 
on  a  hot-water  funnel.  Dry  for  twenty  minutes  at  100°,  and  cool 
down  to  within  15°  to  20°  of  the  solidification-point.  It  is  important 
that  the  fatty  acids  be  thoroughly  dried.  Pour  into  a  test-tube 
100  millimetres  long  and  25  millimetres  in  diameter,  which  is  sus- 
pended by  a  cork  in  the  mouth  of  a  jar  70  millimetres  wide  and 
150  millimetres  high.  A  thermometer,  graduated  in  tenths  of  a 
degree,  between  10°  and  60°,  with  a  bulb  3  centimetres  long   by 


192  PRACTICAL  SANITARY  SCIENCE 

6  millmutivs  diameter,  is  made  to  act  as  a  stirrer.   The  determina- 
tions should  not  vary  by  more  than  o-i°  C. 

4.  TKe  Refractive  Index  :  Oleo-Refractometpy.— The  oleo- 
refractometer  measures  the  rei'ractinn  wiiich  a  ray  of  hght  under- 
goes in  passing  through  a  layer  of  butter.  It  is  found  more  con- 
venient to  read  the  angle  of  total  reflection,  as  indicated  by  the 
sharp  colourless  border-line  which  vertically  intersects  the  scale  of 
the  instrument  between  the  light  and  dark  sections  of  the  field  of 
view.  A  few  drops  of  the  butter-fat  to  be  tested  are  poured  warm 
into  the  prism  of  the  instrument,  and  the  deviation  noted  at  a 
temperature  of  45°  C.  Pure  butter  gives  a  deviation  of  about 
30°  to  the  left.  Certain  forms  of  margarine  give  deviations  much 
less — 15°  and  20° — whilst  cocoa-nut  oil  gives  over  55°. 

The  butyro  -  refractometer  of  Zeiss  is  a  modification  of  the 
Abbe  refractometer,  and  gives  rapid  readings  in  scale  divisions 
which  by  reference  to  a  table  can  be  read  off  as  refractive 
indices . 

5.  Microscopic  Examination. — When  examined  microscopically 
butter-fat  presents  a  collection  of  small  round  refractile  globules, 
together  with  a  few  larger  globules  fairly  uniform  in  size  and  in 
the  number  present  in  a  single  field.  Margarine  presents  a  mass  of 
small  globules  much  less  distinct  in  outline  and  more  crowded 
together.  The  larger  globules  occur  in  relatively  greater  numbers, 
and  present  much  more  diversity  in  size. 

Chemical  Methods  used  in  Analysis  of  Fats :  i.  The  Acid 
Value- — This  is  represented  by  the  number  of  milligrammes  of 
KOH  required  to  neutralize  a  gramme  of  the  fat.  It  is  accordingly 
a  measure  of  the  degree  of  hydrolysis  of  the  fat  which  may  be  due 
to  rancidity  or  to  ferment  action.  Five  to  ten  grammes  of  the  fat 
are  dissolved  in  alcohol  and  titrated  against  tenth  normal  alkali  in 
presence  of  phenolphthalein  or  alkali  blue,  66  of  Meister,  Lucius, 
and  Briining. 

2.  The  Saponification  Value  is  a  measure  of  the  mean  molec- 
ular weight  of  the  fatty  acids  entering  into  the  composition  of  a 
fat.  It  is  to  be  noted  that  in  the  titration  of  fatty  acids  soaps 
are  hydrolysed  by  water,  and  accordingly  react  alkaline;  such 
hydrolysis  is  prevented  if  40  to  50  per  cent,  of  alcohol  be  present. 
The  saponification  value  is  given   by  estimating  the  number  of 


BUTTER  193 

milligrammes  of  KOH  neutralized  in  saponification  of  i  gramme  of 
the  fat  by  the  total  fatty  acids  that  it  contains,  whether  originally 
combined  with  glycerol  or  other  alcohol,  or  free.  Heat  2  grammes 
of  fat  with  25  c.c.  of  alcoholic  potash  in  a  Jena  flask  (glass  that  does 
not  give  off  alkali)  under  a  reflux  condenser  for  half  an  hour.  Carry 
out  a  blank  control  with  the  same  volume  of  alcoholic  KOH  in  a 
similar  flask  lest  the  titre  be  altered  by  COg  or  other  agency  during 
heating.  When  the  saponification  is  complete  titrate  the  alkali  in 
each  flask  with  |  HCl  and  phenolphthalein.  The  difference 
between  the  amounts  of  acid  required  by  the  two  flasks  gives  the 
amount  of  alkali  neutralized  by  the  fatty  acids  contained  in  and 
liberated  during  saponification  from  the  amount  of  fat  taken;  from 
this  the  saponification  value  is  calculated. 

3.  The  Hehner  Value. — This  is  the  percentage  of  fatty  acids 
insoluble  in  water  produced  on  saponification  by  a  fat. 

Two  or  three  grammes  of  the  fat  are  saponified  with  alcoholic 
potash.  The  saponified  mass  is  washed  with  hot  water  into  a  beaker 
on  a  steam  bath,  and  acidified  with  dilute  H2SO4.  When  the 
subjacent  aqueous  layer  has  become  clear,  the  contents  are  filtered 
through  a  weighed  filter;  it  is  well  to  half  fill  the  filter  with  water 
before  pouring  the  fatty  acids  on.  The  beaker  is  washed  with  a 
jet  of  hot  water,  and  the  acids  washed  continuously  as  long  as  any 
acid  reaction  can  be  detected  in  the  washings.  The  filter  with  its 
funnel  are  then  immersed  in  cold  water,  so  that  the  fatty  acids 
solidify;  the  filter  is  dried  and  weighed,  or  when  dry  it  may  be 
extracted  in  a  Soxhlet  apparatus  with  petroleum  ether,  the  ether 
evaporated,  and  the  residue  dried  and  weighed. 

The  Hehner  value  of  butter  is  between  86  and  88,  of  triolein  95-7, 
of  lard  and  most  oils  about  95. 

4.  The  Iodine  Value. — This  value  gives  the  amount  of  halogen 
reckoned  as  iodine  that  the  unsaturated  acids  in  the  fat  take  up, 
expressed  as  a  percentage  by  weight  of  the  fat.  Triolein,  for 
example,  whose  molecular  weight  is  884,  takes  up  6  atoms  of  iodine 
(6  X  127  =  762),  or  86-2  per  cent.;  oleic  acid  has  an  iodine  value  of 
90-1. 

As  saturated  acids  and  their  glycerides  absorb  no  halogen,  the 
iodine  value  is  a  measure  of  the  amount  of  unsaturated  acids 

13 


194  PRACTICAL  SANITARY  SCIENCE 

present.     Acids  with  unsaturated  bonds  in  more  than  one  phice 
absorb  proportionately  more  iodine. 

Determination  by  the  Method  of  Wijs.— Prepare  a  titrated 
sokition  ol  iodine  nionochloridc,  a  titrated  solution  of  sodium 
thiosulphate,  and  a  lo  per  cent,  solution  of  KI. 

The  monochloridc  is  obtained  thus :  Weigh  9-4  grammes  iodine 
trichloride  into  a  300  c.c.  flask,  pour  in  200  c.c.  glacial  acetic 
acid,  fit  the  flask  with  a  cork  through  which  passes  a  CaCL  tube ; 
heat  on  a  water-bath  till  the  contents  are  dissolved.  Weigh 
7-2  grammes  of  iodine,  which  has  been  thoroughly  pulverized  in  a 
mortar,  into  a  second  flask;  w'ash  out  the  mortar  with  glacial  acetic 
acid,  and  heat  this  flask  as  the  other.  Pour  the  contents  of  the  two 
flasks  into  a  stoppered  litre  flask.  Any  undissolved  iodine  is 
fmrther  heated  with  additional  acetic  acid  till  all  is  dissolved  and 
added  to  the  litre  flask.  This  flask  is  then  stoppered  and  allowed 
to  cool;  when  cold,  the  solution  is  made  up  to  a  litre  with  acetic  acid 
and  titrated  next  day.  The  strength  of  the  iodine  chloride  solution 
is  likely  to  alter  a  little  in  the  first  twenty-lour  hours,  but  after  that 
remains  fairly  constant  for  some  weeks  if  care  has  been  taken  to 
exclude  all  water  from  the  glacial  acetic  acid.  To  do  the  titration 
pipette  into  an  Erlenmeyer  flask  exactly  20  c.c.  of  the  iodine 
chloride  solution;  add  about  10  c.c.  of  the  KI  solution  and  about 
300  c.c.  of  water.  Run  in  a  standard  sodium  thiosulphate  solution 
(24  grammes  to  a  litre  standardized  by  Volhard's  method),  and 
finish  off  with  starch  solution.  From  the  amount  of  thiosulphate 
used  the  amount  of  iodine  in  the  measured  amount  of  Wijs's 
solution  is  calculated. 

Estimation  of  the  Iodine  Value  of  the  Fat  or  Fatty  Acid.— 
Weigh  into  a  stoppered  flask  of  100  to  150  c.c.  capacity  a  quantity 
of  the  fat  or  fatty  acid  depending  on  the  iodine  value  of  the  Wijs's 
solution  used  (there  should  be  two  or  three  times  as  much  iodine 
in  the  Wijs  as  the  fat  can  absorb),  say  0-2  to  0-5  gramme,  and 
dissolve  it  in  10  c.c.  CCI4;  add,  say,  25  c.c.  Wijs,  stopper  and  stand 
aside  for  a  couple  of  hours  in  the  dark.  Now  pour  the  contents  of 
the  flask  into  an  Erlenmeyer  (half  to  litre  size) ;  wash  out  any  traces 
of  iodine  with  10  c.c.  of  the  KI  solution  and  afterwards  with 
water;  the  bulk  of  fluid  obtained  should  be  about  300  c.c.  Lastly 
titrate    with   thiosulphate    and   calculate    the    unabsorbed   iodine. 


BUTTER  195 

This  figure,  subtracted  from  the  amount  of  iodine  contained  in  the 
Wijs  used,  gives  the  iodine  absorbed,  which  is  readily  calculated 
into  a  percentage  of  the  amount  of  fat  taken. 

5.  The  Acetyl  Value. — This  determination  gives  the  number 
of  milligrammes  of  caustic  potash  required  to  neutralize  the  acetic 
acid  liberated  when  i  gramme  of  acetylated  fat  or  fatty  acids  is 
saponified. 

Those  fatty  acids  in  a  fat  or  oil  which  are  hydroxy  become 
acetylated  when  heated  with  acetic  anhydride: 

RC<^2"^.C00H  +  CH^'CO/^"  RC/^^^^CO.O  (,QQj^  ^  CH3COOH. 

The  number  of  acetyl  radicals  taken  up  depends  on  the  number 
of  hydroxy  acids  present,  and  the  number  of  hydroxyl  groups 
contained.  On  saponification,  the  acetyl  groups  are  split  off  as 
acetic  acid,  and  the  amount  of  acetic  acid  so  liberated  is  a  measure 
of  the  hydroxyl  groups. 

Heat  5  to  10  grammes  of  the  fat  or  fatty  acids  with  twice  the 
weight  of  acetic  anhydride  in  a  flask  under  a  reflux  condenser  for 
a  couple  of  hours.  Transfer  the  contents  to  a  large  beaker,  and 
add  I  litre  of  boiling  water.  Heat  for  half  an  hour  whilst  a  stream 
of  CO2  is  led  through  to  prevent  bumping.  Separation  is  allowed 
to  take  place,  and  the  watery  layer  is  syphoned  off.  Salt  may  be 
added  if  the  oily  layer  does  not  separate  easily.  More  water  is 
added,  and  in  turn  syphoned  off  till  the  acetic  acid  formed  from 
the  excess  of  anhydride  has  all  been  removed.  Filter  through  a  dry 
filter  in  a  drying  oven  to  remove  water. 

Weigh  3  to  5  grammes  of  the  acetylated  product ;  saponify  with  a 
known  amount  of  KOH  and  determine  the  saponification  value. 
Free  the  soap  from  alcohol  by  evaporation,  and  estimate  the  acetic 
acid  as  follows :  Add  an  excess  of  10  per  cent.  HgSO^,  and  distil  the 
liquid  in  a  current  of  steam.  Collect  the  distillate  until  100  c.c. 
require  not  more  than  o-i  c.c.  of  decinormal  alkali  to  neutralize  it. 
More  than  600  c.c.  of  distillate  will  generally  be  obtained.  Titrate 
this  with  decinormal  alkali  (phenolphthalein  indicator),  and  multiply 
the  number  of  c.c.  used  by  5-61;  divide  the  product  by  the  weight 
of  the  acetylated  product  used  to  get  the  acetyl  value. 

6.  The  Reichert-MeiSSl  Value.— This  is  that  usually  applied  for 
identification  of  butter-fat.     It  is  a  measure  of  the  amount  of  lower 


196  PRACTICAL  SAXITARY  SCIENCE 

fatty  acids  in  a  fat  which  volatilize  in  a  current  of  steam.  The 
value  is  expressed  b\'  the  number  of  c.c.  of  -^^^  alkali  required  to 
neutralize  the  volatile  fatty  acids  liberated  under  certain  prescribed 
conditions  from  5  grammes  of  the  fat.  In  this  country  the  Wollny 
modification  is  used.  Most  fats  and  oils  in  the  fresh  state  contain 
only  traces  of  volatile  acids  or  their  glycerides,  and  give  values  less 
than  one.  Cocoa-nut  oil  gives  Reichert-Meissl-Wollny  value  5  to 
8;  butter  a  notable  exception  possessing  a  value  26  to  32,  Some 
porpoise  oils  are  said  to  reach  60. 

The  estimation  is  a  comparative  one,  and  that  only  whilst  the 
conditions  are  accurately  observed. 

Weigh  5  grammes  of  prepared  butter-fat  into  a  flat-bottomed 
flask  of  300  c.c.  capacity,  having  a  neck  7  to  8  centimetres  long  by 
2  centimetres  wide.  Add  2  c.c.  NaOH  solution  prepared  by  dis- 
solving 98  per  cent.  NaOH  in  an  equal  weight  of  water  (protected 
from  the  action  of  atmospheric  COo)  and  10  c.c.  92  per  cent,  alcohol. 
Heat  the  flask  on  a  boiling  bath  for  fifteen  minutes  under  a  reflux 
condenser.  Remove  the  condenser,  and  drive  off  the  alcohol  com- 
pletety  by  heating  further  for  half  an  hour.  Add  100  c.c.  of  water 
which  has  been  boiled  (to  remove  CO.,).  and  heat  till  the  soap  dis- 
solves. Add  40  c.c.  of  normal  sulphuric  acid  and  some  bits  of 
pumice  or  porous  clay,  and  connect  the  flask  with  a  condenser  tube 
7  millimetres  in  diameter,  surrounded  by  a  water-jacket  35  centi- 
metres long  by  means  of  a  bent  tube  15  centimetres  long  from  the 
cork  of  the  flask  to  the  bend  of  the  tube,  on  the  middle  of  which  a 
bulb,  5  centimetres  in  diameter,  is  blown.  The  flask  is  heated  on 
an  asbestos  board,  with  an  opening  in  its  centre  5  centimetres  in 
diameter,  by  a  small  flame  till  the  insoluble  acids  are  melted.  When 
fusion  is  complete  the  heat  is  increased,  and  no  c.c.  are  distilled  in 
about  thirty  minutes  into  a  graduated  flask.  Shake  the  distillate 
and  filter  off  100  c.c.  into  a  beaker;  add  0-5  c.c.  of  a  i  per  cent, 
solution  of  phenolphthalein  in  alcohol,  and  titrate  with  —  soda  or 
baryta.  Carr}'  out  a  blank  experiment  with  the  same  quantities  of 
everything  except  fat ;  the  amount  of  ^^^  alkali  required  to  neutralize 
the  distillate  should  not  exceed  0-2  to  0-3  c.c.  The  number  of  c.c. 
decinormal  alkali  used,  less  the  blank,  multiplied  by  i-i,  gives  the 
Reichert-Meissl-Wollny  number. 

Leffmann  and  Beam  employ  20  c.c.  of  glycerol  instead  of  the 


BUTTER  197 

alcohol  used  by  Wollny.  They  heat  the  fat  with  glycerol  and  soda 
for  eight  minutes,  when  the  fluid  becomes  clear  and  is  allowed  to 
cool  to  about  80°  C.  Then  90  c.c.  of  water  at  about  80°  C.  and 
50  c.c.  of  a  2'5  per  cent.  H2SO4  solution  are  added,  and  the  process 
is  finished  as  above. 

In  this  distillation  only  a  part  of  the  volatile  acids  distils  over 
[87  per  cent,  of  total  volatile  acids  (according  to  Richmond) ;  88  per 
cent,  butyric,  88  to  100  per  cent,  caproic,  24  to  25  per  cent,  capryllic 
(according  to  Jensen)]. 

Five  grammes  of  pure  butter-fat  give  a  number  never  less  than 
24,  margarine  never  more  than  3. 

In  order  to  prevent  fraud  not  more  than  10  per  cent,  of  butter-fat 
is  permitted  in  margarines,  which  will  produce  a  Reichert-Wollny 
number  of  4. 

Example. — In  a  mixture  of  margarine  and  butter-fat  the  Reichert- 
Wollny  figure  is  16;  find  the  percentage  of  butter-fat. 

Taking  3  as  the  highest  possible  figure  for  margarines,  and  24 

as  the  lowest  for  butter-fats,  21  (24-3)  will  represent  100  per  cent. 

of  pure  butter-fat. 

21    :  16-3   :  :  100   :  x. 

13  X 100     ,  , 

x=-^ =62  nearly. 

21  ^ 

This  sample,  therefore,  contains  62  per  cent,  of  butter-fat,  and 
consequently  38  per  cent,  of  margarine. 

The  Polenske  Number. — This  number  represents  the  volatile 
fatty  acids  insoluble  in  water.  It  is  much  used  in  detecting  cocoa- 
nut  oil  in  butter  and  other  fats.  It  may  be  determined  with  the 
Reichert-Meissl  figure  in  one  weighed  portion  of  the  fat. 

Saponify  5  grammes  of  prepared  fat  with  20  grammes  of  glycerol 
and  2  c.c.  of  a  50  per  cent.  NaOH  solution.  This  requires  about 
five  minutes,  and  is  complete  when  the  liquid  is  quite  clear.  While 
still  hot  add  90  c.c.  of  boiled  water,  at  first  drop  by  drop,  to  prevent 
frothing,  and  shake  till  the  soap  is  dissolved.  Warm  to  50°,  and 
add  50  c.c.  dilute  H2SO4  (25  c.c.  to  a  litre)  and  ^  gramme  of  granu- 
lated pumice  (grains  i  millimetre  in  diameter).  Connect  with  dis- 
tilling apparatus  used  in  the  Reichert-Meissl  method,  and  distil 
over  no  c.c.  in  twenty  minutes.  Cool  the  flask  by  immersion  in 
water  at  15°  C.     Stopper  it,  and  invert  four  or  live  times.     Filter 


198  PRACTICAL  SANITARY  SCIENCE 

through  a  dry  lilter  fitted  close  to  the  funnel  (loo  c.c.  of  the  filtrate 
may  be  titrated  for  the  Reichert-Meissl  number).  Wash  the 
material  on  the  lilter  with  three  15  c.c.  portions  of  water,  each  of 
which  have  washed  out  the  flask  and  the  condenser.  Dissolve  the 
fats  on  the  filter  with  three  15  c.c.  portions  of  neutral  90  per  cent, 
alcohol.  Titrate  the  united  alcoholic  washings  ^^'ith  -j^  barium 
hydrate,  using  phenolphthalein  as  indicator.  The  number  of  c.c. 
used  is  the  Polenske  number. 

Samples  of  butter  possessing  Reichort-]\Ieissl  figures  25  to  30 
will  give  Polenske  numbers  of  1-5  to  3. 

Samples  of  cocoa-nut  oil  of  Reichert-IMeissl  values  6  to  7  will 
give  Polenske  figures  16  to  17. 

Lard  and  tallow  give  Reichert  and  Polenske  tigures  of  about 
0-5  each. 

Valenta's  Test. — \'alenta  demonstrated  the  fact  that  there  is 
a  considerable  difference  in  the  temperatures  at  which  various  fats 
dissolve  without  turbidity  in  acetic  acid. 

Weigh  out  275  grammes  of  butter- fat  into  a  test-tube;  add 
3  c.c.  99-5  per  cent,  acetic  acid;  insert  a  thermometer,  and  gently 
heat  with  vigorous  shaking  until  the  mixture  becomes  transparent. 
Now  cool  down  gradually,  stirring  with  the  thermometer  until  the 
first  trace  of  opacity  makes  its  appearance,  generallj^  as  a  fine  tail 
in  the  fluid  at  the  extremity  of  the  thermometer's  bulb.  This  is 
the  required  temperature.  The  glycerides  of  the  saturated  fatty 
acids  are  deposited  as  the  acetic  acid  cools.  The  temperature 
corresponding  with  pure  butter-fats  runs  from  29°  C.  to  39°  C, 
and  that  for  margarine  falls  between  94°  C.  and  97°  C.  A  standard 
sample  of  butter  may  be  tested  against  a  weaker  acid  giving  a 
temperature  of  turbidity  of,  say,  60°  C.  Margarine  then  gives 
100°  C.  or  over.  This  is  a  very  good  preliminary  test  for  the 
differentiation  of  pure  butters  from  margarine. 

Examination  under  Polarized  Light. — A  small  particle  of 
butter  is  placed  on  a  clean  microscopic  slide,  and  a  cover-glass 
affixed.  The  slide  is  placed  on  the  stage  of  a  microscope  provided 
with  crossed  nicols,  and  examined  with  a  coarse  objective.  In 
order  to  shut  out  light  from  the  upper  surface  a  short  black  tube 
is  laid  on  the  slide  in  such  a  manner  that  the  objective  dips  into  it. 
When  pure  butter-fat,  which  is  non-crystalline,  is  examined,  it  pre- 


BUTTER  199 

scnts  a  uniformly  dark  jicld.  On  the  otlicr  hand,  when  margarine  is 
examined,  certain  portions  of  the  field  arc  bright,  and  crystalline 
masses  are  dimly  perceived.  These  may  be  critically  studied  by 
uncrossing  the  nicols. 

To  Detect  Cottonseed  Oil  in  Butter.— To  the  melted  fat  add 
an  equal  volume  of  a  saturated  solution  of  lead  acetate,  and  a 
smaller  quantity  of  ammonia,  and  stir.  On  standing  for  a  little 
time  the  superficial  layers  turn  orange-red. 

Bechi's  Silver  Test. — Dissolve  i  gramme  AgNOg  in  100  c.c.  of 
95  per  cent,  alcohol;  add  20  c.c.  ether  and  a  drop  of  HNO3,  and 
thoroughly  mix.  To  10  c.c,  of  the  sample  of  fat  add  2  c.c.  of  this 
reagent.  Mix  and  stand  the  test-tube  in  boiling  water  for  fiifteen 
minutes.  The  mixture  assumes  a  considerably  darker  tint,  due 
to  reduced  silver,  in  the  presence  of  cottonseed  oil.  These  tests 
are  best  performed  in  the  presence  of  blank  tests  on  pure  butter- fat. 

Halphen's  Test. — Mix  equal  vcrlumes  of  amyl  alcohol  and  CSg  in 
which  I  per  cent.  S  has  been  dissolved.  To  5  c.c.  of  this  mixture 
add  an  equal  volume  of  the  fat  in  a  test-tube,  and  heat  in  a  bath 
of  boiling  saturated  brine  for  fifteen  minutes.  A  deep  red  or 
orange  colour  is  produced  in  the  presence  of  cottonseed  oil.  In  its 
absence  little  or  no  colour  is  developed.  Pyridin  in  the  amyl 
alcohol  appears  to  be  the  active  reagent. 

Sesame  Oil. — Fats  containing  this  oil  give  a  red  colour  when 
heated  with  stannous  chloride  on  a  water-bath.  The  coloxir  is  not 
discharged  by  moderate  dilution  with  water,  thereby  differing  from 
the  colour  produced  by  turmeric. 

Baudouin' s  Test. — Dissolve  o-i  gramme  cane-sugar  in  10  c.c.  HCl 
(specific  gravity  1-2).  Add  to  the  solution  in  a  test-tube  20  c.c.  of 
the  fat  and  shake  thoroughly  for  a  minute.  Allow  to  stand  till  the 
oil  separates  from  the  aqueous  solution.  In  the  presence  of  i  per 
cent,  sesame  oil  the  aqueous  solution  is  coloured  deep  red. 

Colouring^  Matters.- — Annatto,  turmeric,  and  some  coal-tar  pro- 
ducts have  been  used  to  increase  the  yellow  tint  of  butter.  These 
colouring  matters  are,  for  the  most  part,  vegetable,  and  harmless. 
If  the  colouring  matter  can  be  extracted  with  alcohol  it  is  foreign, 
since  the  natural  colouring  matter  of  butter  is  not  soluble  in  alcohol. 
Coal-tar  dyes  may  be  fixed  on  silk  or  wool  by  boiling  fibres  in  the 
alcoholic  extract  diluted  with  water  and  acidified  with  HCl. 


200  PRACTICAL  SANITARY  SCIENCE 

If  saffron  be  present,  the  alcoholic  extract  will  be  coloured  green 
by  HXO3,  and  red  by  HCl  and  sugar. 

Tunueric  is  detected  by  evaporating  the  alcoholic  extract  to 
dryness,  and  boiling  the  residue  in  a  few  c.c.  of  dilute  boric  acid 
solution.  A  strip  of  filter-paper  soaked  in  the  latter  and  slowly 
dried  becomes  cherry  red.  Addition  of  a  drop  of  alkali  turns  the 
red  to  olive  green. 

In  recent  years  a  number  of  liquid  fats  have  been  hydrogenated 
by  the  catal^'tic  action  of  nickel  and  other  catalysts — oleic  acid,  e.g., 
becoming  stearic  acid — Ci8H3402  +  H2=  CjgHggO.^.  The  physical 
change  from  liquid  to  solid  has  enabled  manufacturers  to  incorporate 
various  oils  in  margarines  and  butter.  Whether  such  hardened  fats 
are  equally  digestible  and  equally  nutritious  with  the  natural 
bodies  they  now  chemically  represent  remains  to  be  seen.  Their 
appearance  has  caused  considerable  trouble  to  analysts,  as  many 
of  the  ph^-sical  and  chemical  constants  have  been  completely  upset. 

Bacteria  in  Butter. — Economic  bacteria  take  part  in  the  conver- 
sion of  cream  into  butter.  In  Europe  and  America  much  butter  is 
made  from  pasteurized  cream,  to  which  '  starters  '  (cultures  of 
lactic  acid  bacteria)  are  added.  By  this  means  the  process  of 
butter-making  is  much  better  controlled,  and  results  are  much 
more  uniform.  British  butter  contains  from  1,000,000  to  50,000,000 
micro-organisms  per  gramme.  The  bulk  of  these  are  Bacillus  acidi 
lactici,  B.  lactis  aerogenes,  etc.,  which  keep  in  check  the  development 
of  unfavourable  bacteria,  such  as  B.  mesenfericus,  B.  fluorescens, 
B.  suhtilis,  etc.,  which  give  origin  to  evil  flavours,  bitter  taste,  and 
rancidity. 

The  principal  pathogenic  organism  found  in  butter  is  the  B. 
tuberculosis.  To  detect  this  organism  warm  a  sample  of  butter  to 
42°  C.  Centrifugalize  the  liquid,  and  inoculate  guinea-pigs  with 
the  sediment.  It  is  of  importance  to  note  that  the  butter  bacillus 
of  Rabinowitsch  and  Petri  is  acid-fast,  and  morphologically  like 
the  tubercle  bacillus;  and,  moreover,  when  injected  intraperi- 
toneally  mixed  with  butter,  it  produces  similar  lesions  in  guinea- 
pigs.  It  is,  however,  readily  distinguished  from  B.  fttberctdosts  by  its 
rapid  growth  on  glycerine  agar  and  other  ordinary  media,  forming 
an  abundant  dry  mass  in  three  or  four  days. 


CHEESE 


CHEESE 


Cheese  consists,  for  the  most  part,  of  proteins  and  fat.  It  may 
be  prepared  (i)  by  adding  rennet  to  milk,  whereby  the  casein  clots 
and  entangles  most  of  the  fat;  and  (2)  by  allowing  the  milk  to 
become  sour  through  the  formation  of  lactic  acid,  or  by  the  addition 
of  a  dilute  acid,  such  as  vinegar,  when  the  cheese  contains  little  fat. 

The  characters  of  different  cheeses  depend  on  the  kinds  of  milk 
used,  the  methods  of  preparation  employed,  and  the  types  of 
micro-organism  admitted  to  the  original  milk  or  to  the  cheese 
whilst  ripening.  During  the  ripening  of  cheese  a  partial  digestion 
of  proteins  is  effected,  resulting  in  the  production  of  the  so-called 
primary  products  of  digestion — albumoses  and  peptones.  Later, 
secondary  products  of  ripening  are  found — viz.,  amido-compounds 
and  ammonia. 

Whether  during  these  changes  fat  is  increased  at  the  expense  of 
protein,  as  was  once  believed,  is  doubtful.  The  relative  propor- 
tions of  this  digestive  work  carried  out  respectively  by  milk  enzymes 
and  by  enzymes  of  added  bacteria  are  unknown.  The  flavour  of  a 
particular  cheese  is  due  to  the  micro-organisms  growing  in  it  during 
ripening.  The  old  idea  that  a  particular  cheese,  such  as  Stilton, 
can  be  made  only  in  one  locality  is  exploded.  Magnificent  Stiltons 
are  now  made  in  Hampshire  by  the  agency  of  a  '  cheese  mould  ' 
carried  to  that  county  from  Leicester. 

Soft  cheeses,  such  as  Brie  and  Camembert,  are  produced  by 
clotting  milk  with  rennet  at  temperatures  below  30°  C,  and  using 
little  pressure.  Hard  cheeses,  like  Stilton,  Cheddar,  Gorgonzola, 
and  Gruyere,  are  clotted  at  higher  temperatures — 30°  to  35°  C. — 
and  submitted  to  greater  pressure.  Soft  cheeses  contain  much 
water,  and  therefore  fail  to  keep  long. 

The  nitrogen  of  the  proteins  in  cheese  exists  in  a  variety  of  forms. 
Van  Slyke  found  that  the  3-86  per  cent.  N  of  an  American 
Cheddar  was  distributed  as  follows:  Water-soluble  N  1-46,  para- 
casein-mono-lactate  0-94,  paranuclein  0-14,  caseoses  0-22,  peptones 
0'i8,  amides  0-79,  and  ammonia  0-13. 

A  full-cream  cheese  contains  30  to  35  per  cent,  butter-fats. 
Filled  cheeses  may  contain  any  proportions  of  foreign  fats  mixed 
with  butter-fats. 


202  PRACTICAL  SAXITARY  SCIENCE 

If  the  fat  is  considerably  less  than  the  protein,  the  cheese  was 
made  from  skimmed  milk. 

fat 

In  a  whole-milk  cheese  the  ratio  ^     r^^,  is  greater  than  i 

6-37  total  N 

(generally  1-25  to   1-5).     In  a  skimnied-milk  cheese  this  ratio  is 
less  than  i. 

The  digestibility  of  cheese  in  the  stomach  is  less  than  that  of 
meat,  on  account  of  its  proteins  being  covered  with  fat.  Cheese 
should  therefore  be  well  masticated,  or,  better,  thoroughly  grated 
before  being  used.  Its  digestion  in  the  small  intestine  is  effected 
without  difficulty.  Owing  to  the  small  quantity  of  water  con- 
tained in  cheese  compared  with  that  in  beef,  it  has  a  higher  nutritive 
value  than  the  latter.  The  energy  derivable  from  cheese,  as 
measured  b}'  calories,  is  about  three  times  that  of  beef.  More- 
over, the  fact  that  the  protein  of  cheese  is  chiefly  casein,  and 
accordingh'  purin-free,  should  highly'  recommend  it  as  an  article 
of  diet  to  those  who  are  in  any  wa}-  troubled  by  uric  acid. 

Percentagre  Composition  of  a  Few  Soft  Cheeses : 

Camembert 

Brie 

Stracchino   . . 


Water. 

Proteins. 

Fat. 

Ash. 

50-9 

i8-6 

27-4 

3-1 

50-0 

i8-3 

27-6 

4-1 

39-2 

29-3 

277 

3-8 

of  a 

Few  Hard  Cheeses: 

Water. 

Proteins. 

Fat. 

Ash. 

27-2 

36-6 

32-0 

4-2 

30-4 

36-1 

287 

4-8 

28-6 

35-6 

31-8 

4-0 

32-0 

35-1 

28-1 

4-8 

Cheddar 

Cheshire 

Stilton 

Gruyere        .... 

The  ripening  of  cheese  has  been  somewhat  differently  explained 
by  Freudenreich,  Duclaux,  and  Babcock  and  Russell.  When  the 
curd  is  thrown  down  by  rennet,  it  carries  with  it  most  of  the  bacteria 
of  the  milk.  Freudenreich  believes  that  the  lactic  acid  organisms, 
which  develop  early  and  rapidly,  are  the  chief  factors  in  the  process 
of  ripening.  Duclaux  holds  that,  since  the  ripening  proceeds  after 
the  lactic  acid  organisms  have  considerably  diminished,  the  active 
agents  are  enzymes  secreted  by  a  variety  of  organisms,  which  he 


CHEESE  203 

names    Tyrothrix.     Babcock    and    Russell    ac(:c[)t    the    view    that 
ripening  is  effected  by  an  enzyme  originally  present  in  milk. 

Moulds  in  Cheese. — Green  mould  [Penicillium  glaucum)  is 
found  in  Roquefort  and  Gorgonzola.  Aspergillus  glaucus  pro- 
duces the  appearance  known  as  blue  mould,  whilst  red  mould  is 
accounted  for  by  the  growth  of  Sporendonema  casei.  The  common 
mould  {Mucor  mucedo)  is  found  in  more  than  one  variety. 

Of  animal  parasites  found  in  cheese,  the  two  most  frequently 
met  with  are  '  the  cheese  mite  '  {Acarus  domesficus),  and  '  cheese 
maggots  '  (larv?e  of  Piophila  casei). 

Adulteration  in  Cheese.  —  The  principal  adulterations  in 
cheese  are  the  use  of  skimmed  milk  for  whole  milk,  and  the  addition 
to  skimmed  milk  of  foreign  fats.  Mineral  adulterants,  such  as 
chromate  of  lead,  used  to  tint  the  rind  and  sulphate  of  zinc  ('  cheese 
spice  '),  used  to  prevent  gas  formation  from  fermentation,  are  rarely 
met  with. 

Estimation  of  Water  in  Cheese. — Dry  5  grammes  cut  into 
thin  slices  in  an  air  oven  at  100°  C.  to  constant  weight.  Loss  of 
weight  equals  water.- 

Ash. — Ignite  the  residue  from  the  water  determination  at  a  low 
red  heat;  cool  in  a  desiccator  and  weigh. 

Fat.— Place  50  grammes  of  cheese  in  a  muslin  bag  in  a  beaker  on 
a  water-bath;  the  fat  will  pass  out  in.  a  pure  state  into  the  beaker. 
Perform  the  Valenta  and  Reichert-Meissl  tests  on  this  (as  described 
under  Milk)  to  detect  and  estimate  amounts  of  pure  butter- fats  and 
foreign  fats. 

The  total  fat  is  estimated  as  follows:  Grind  5  grammes  of  cheese 
in  a  mortar  with  10  grammes  of  anhydrous  copper  sulphate ;  place  a 
layer  of  anhydrous  copper  sulphate  about  2  centimetres  thick  on 
the  bottom  of  the  receiver  of  a  Soxhlet ;  add  the  ground  mixture,  and 
rinse  the  mortar  with  a  little  of  the  ground  sulphate  and  afterwards 
with  ether.  Extract  for  sixteen  hours.  Evaporate  the  ether  from 
the  extraction  flask,  and  dry  the  fat  in  a  steam-chest  to  constant 
weight. 

Werner-Schmidt  Method. — Boil  2  grammes  of  cheese  with 
5  CO.  of  water  and  10  c.c.  of  concentrated  HCl  in  a  large  test-tube, 
with  constant  shaking  until  all  but  the  fat  is  dissolved.  Cool;  add 
25  c.c.  ether,  and  shake  well.     When  separated,  draw  off  as  much 


204  PRACTICAL  SANITARY  SCIENCE 

as  possible  of  the  ether.  Extract  with  four  additional  portions 
of  ether,  and  collect  the  whole  in  a  flask.  Distil  off  the  ether  and 
weigh  the  fat. 

Proteins. — Treat  I  gramme  of  cheese  by  the  Kjeldahl  method. 
N  X  6-25  =  proteins. 

Separation  and  Determination  of  N  Compounds  (Van  Slyke). 
Mix  25  grammes  of  cheese  with  an  equal  weight  of  quartz  sand  in  a 
mortar,  and  transfer  to  a  flask;  add  about  100  c.c.  of  water  at 
50^,  and  keep  the  temperature  at  50°  to  55""'  for  half  an  hour,  shaking 
frequently  the  while  Decant  the  liquid  through  a  cotton  filter 
into  a  500  c.c.  graduated  flask.  Treat  the  residue  with  repeated 
portions  of  100  c.c.  of  water  in  the  same  manner  until  the  water 
extract  amounts  to  just  500  c.c.  Employ  aliquot  parts  of  this  for 
the  various  estimations. 

Watcr-Soliihle  N. — Perfonn  the  Kjeldahl  process  on  50  c.c.  of  the 
water  extract  (  =2-5  grammes  of  cheese). 

Para-Niiclein  N. — To  100  c.c.  water  extract  add  5  c.c.  of  a  i  per 
cent.  HCl  solution;  stand  at  50°  to  55°  till  separation  is  complete,  as 
shown  by  a  clear  supernatant  liquid.  Filter,  wash  the  precipitate 
with  water,  and  determine  the  N  by  Kjeldahl. 

N  as  Coagiilahle  Protein. — Neutralize  the  filtrate  from  the  last 
determination  with  dilute  KOH;  heat  at  100°  till  the  coagulum,  if 
any,  settles  out  completely.  Filter,  wash  the  precipitate,  and 
determine  the  N  in  it  as  above, 

N  as  Caseoses. — Treat  the  filtrate  from  the  preceding  with  i  c.c. 
of  50  per  cent,  sulphuric  acid,  saturated  with  ZnS04,  and  warm  to 
65°  to  70°  until  the  caseoses  settle  out  completely.  Cool,  filter, 
wash  with  saturated  ZnSOj  acidified  with  H2SO4,  and  determine  the 
N  in  the  precipitate. 

N  as  Amides  and  Peptones. — Put  100  c.c.  of  water  extract  in  a 
250  c.c.  graduated  flask,  add  i  gramme  NaCl  and  a  12  per  cent, 
solution  of  tannin  till  a  drop  added  to  the  clear  supernatant  solution 
fails  to  produce  further  precipitation;  dilute  to  the  mark,  shake, 
and  pour  on  a  dry  filter;  determine  the  N  in  50  c.c.  of  the  filtrate  = 
N  in  amido-acid  and  ammonia  compounds.  This  minus  the 
ammonia  N  =  amido-X.  Peptone  N  =  total  N  in  water  extract 
minus  sum  of  para-nuclein  X,  coagulable  protein  X,  and  X  of 
caseoses,  amides,  and  ammonia. 


CHEESE  205 

A^  as  Ammonia. — Distil  100  c.c.  of  the  filtrate  from  the  tannin- 
salt  precipitation  into  standard  acid,  and  titrate  against  standard 
alkali, 

N  as  Para-Casein  Lactate. — Wash  the  insoluble  residue  produced 
in  obtaining  the  water  extract  with  several  portions  of  a  5  per  cent. 
NaCl  solution  to  form  a  500  c.c.  salt  extract;  determine  the  N  in 
an  aliquot  part  of  this  salt  extract. 

Determination  of  Lactose. — Boil  25  grammes  of  finely  divided 
cheese  with  two  portions  of  100  c.c.  each  water.  Pour  on  filter, 
wash  residue  with  hot  water,  make  up  the  watery  extract  to  250  c.c, 
and  determine  the  lactose  by  the  Fehling  or  Pavy-Fehling  method. 

Detection  of  Foreigrn  Fat. — Submit  the  prepared  fat  to  the 
Reichert-Meissl  method. 

Detection  of  Bacillus  Tuberculosis. — Rub  up  portions  from 
the  central  parts  of  the  cheese  with  sterile  normal  saline  until  a 
good  emulsion  is  obtained.  Strain  through  sterile  absorbent  cotton, 
and  inject  the  equivalent  of  2  grammes  of  cheese  into  each  of  two 
or  three  guinea-pigs. 

Lard. — Freshly  rendered  lard  (internal  abdominal  fat  of  pig)  con- 
tains no  free  fatty  acids.  It  is  much  adulterated  with  cottonseed 
oil  and  beef  stearin.  It  has  the  following  constants :  Melting-point, 
36°  to  45°  C;  iodine  absorption,  50  to  65  per  cent.;  saponification 
value,  195  to  197;  Zeiss  butyro-refractometer  at  40°  C.  =48-8°  to 
51°;  specific  gravity  at  15-5°  C,  0-931  to  0-932. 

If  the  iodine  value  fall  outside  the  above  limits,  the  lard  is  adulter- 
ated, but  a  normal  iodine  figure  is  no  guarantee  of  genuineness,  as  a 
judicious  mixture  of  cottonseed  arachis  or  other  oil,  with  beef 
stearin,  will  give  normal  values  when  tested. 

Infants'  Foods.- — The  market  is  flooded  with  a  large  number  of 
products  of  very  varying  composition.  If  the  milk  preparations 
(condensed,  dried,  and  humanized  milks)  be  grouped  as  a  class,  all 
the  other  foods  contain  flours  in  which  the  starch  is  altered  or 
unaltered,  or  capable  of  being  altered  or  otherwise  during  prepara- 
tion of  the  food.  It  is  necessary  to  determine  the  presence,  nature, 
and  amount  of  unaltered  starch,  the  extent  to  which  the  starch  is 
converted  during  the  preparation  of  the  food  according  to  instruc- 
tions on  the  label,  the  presence  or  absence  of  diastase  in  active 
form,  and  the  nature  of  the  cereal  from  which  the  starch  is  derived. 


2o6  PRACTICAL  SAXITARY  SCIENCE 

Witli  the  exception  of  full-cream  dried  milks  and  full-cream  con- 
densed milks,  it  may  be  fairly  stated  that  practically  all  the  infants' 
foods  advertised  are  highly  deficient  in  fat,  and  many  deficient  in 
proteins. 

The  only  physiologically  suitable  food  for  a  young  mammal  is  the 
milk  of  its  mother  or  some  other  animal  of  the  same  species. 

The  chemical  composition  of  a  foodstuff  is  no  criterion  of  its 
nutritional  value.  Due  proportion  of  protein  carbohydrate  and  fat 
does  not  constitute  a  correct  diet.  For  example,  the  proteins  of 
different  milks  \"ary  because  of  the  fact  that  milks  have  a  develop- 
mental as  well  as  nutritive  function:  accordingly  milks  of  different 
species  are  not  interchangeable.  It  is  known  that  the  milk  of 
animals  whose  chief  digestion  is  gastric  (cow,  goat,  etc.)  forms 
solid  clots  of  casein,  \\hilst  that  of  animals  whose  chief  digestion  is 
intestinal  (mare,  etc.)  does  not  form  solid  clots,  but  soft  gelatinous 
masses,  which  easil}'  traverse  the  stomach  and  intestine. 

The  digestion  of  infants  is  largely  intestinal,  and  human  milk  is 
the  onl}^  form  which  in  the  early  days  puts  no  strain  on  it.  It  is 
common  clinical  knowledge  that  infants  in  the  first  months  of  life 
fed  on  artificial  foods  containing  starch  become  the  subjects  of 
scurv^',  atrophy,  and  gastro-intestinal  disorders.  The  process  of 
digestion  is  accompanied  by  the  liberation  of  considerable  potential 
energy-,  and  in  the  case  of  the  infant  with  little  energy  to  lose  the 
digestion  of  an  artificial  food,  containing  in  addition  to  a  foreign 
milk  starch  only  partially  converted,  there  may  not  be  nearly 
sufficient  energy  to  meet  the  largely  increased  call,  with  the  well- 
kno\vn  accompaniments  of  this  failure — grave  nutritional  dis- 
turbance, rachitis,  scurvy,  anaemia,  and  more  than  one  form  of 
profound  gastro-intestinal  fermentation. 

Estimation  of  Starch:  i.  Direct  Conversion  by  Acid.— 
Hemicellulose  and  all  carbohydrates  capable  of  conversion  to  sugar 
are  included  with  starch. 

Wash  2  grammes  of  the  finely  divided  material  on  a  filter  with 
ether,  using  lo  c.c.  four  or  five  times;  continue  the  washing  with 
first  100  c.c.  10  per  cent,  alcohol,  and  then  with  lo  c.c.  absolute 
alcohol.  Now  wash  off  the  contents  of  the  filter  into  a  flask  with 
150  c.c.  water  and  20  c.c.  HCl  (specific  gravity,  1-125).  Place  the 
flask  on  a  boiling-water  bath  under  a  reflux  condenser  for  two  hours. 


CHEESE  207 

Cool,  neutralize  with  NaOH,  add  alumina  cream  if  necessary, 
mix,  make  up  to  |  litre,  filter,  and  estimate  the  dextrose  in  an 
aliquot  part  of  the  filtrate  by  the  polarimeter  or  by  Fehling's 
method.  Calculate  the  dextrose  figure  into  starch  by  multiplying 
it  by  o-g. 

2.  Conversion  by  Diastase. — By  this  method  starch  only  is 
acted  on;  hence  in  the  presence  of  other  substances  it  is  to  be 
recommended.  Starch  is  first  converted  into  maltose  and  dextrin, 
and  finally  into  glucose. 

Prepare  2  grammes  with  ether  and  alcohol  as  above.  Wash  off 
the  filter  into  a  beaker  and  boil  for  fifteen  minutes,  or  until  com- 
pletely gelatinized,  stirring  constantly.  Cool  to  55°,  and  add 
sufficient  malt  extract  (10,  15,  20  c.c,  according  to  degree  of 
activity),  or  better  animal  diastase,  and  digest  for  an  hour  at  55^. 
Boil  for  fifteen  minutes,  add  further  animal  diastase,  replace  water 
lost  by  evaporation,  and  digest  for  another  hour,  or  until  when 
treated  with  iodine  under  the  microscope  no  starch  appears.  Cool, 
make  up  to  250  c.c,  add  20  c.c.  HCl  (specific  gravity,  1-125),  S-^id 
proceed  as  in  the  acid  conversion  method. 

Reducing  Sugars  as  Dextrose  (Lactose  excepted). — ^A  cold- 
water  extract  is  made  and  titrated  with  Fehling's  solution. 

Lactose. — Baker  and  Hulton  have  shown  that  an  aqueous  solu- 
tion of  lactose,  unlike  maltose,  dextrose,  cane-sugar,  etc.,  is  not 
fermented  by  ordinary  brewer's  yeast;  hence  small  amounts  of 
lactose  added  to  flours,  etc.,  can  be  estimated  by  measuring  the 
reducing  action  on  Fehling's  solution  of  the  residue  after  fermen- 
tation. 

Boil  the  aqueous  extract  with  2  per  cent,  of  citric  acid  to  invert 
any  cane-sugar,  thus  facilitating  fermentation ;  neutralize ;  cool  and 
add  a  little  cold  aqueous  extract  of  diastatic  malt.  Close  the  con- 
taining flask  with  cotton-wool,  and  incubate  at  27°  C.  for  seventy- 
two  hours.  The  solution,  now  destitute  of  all  reducing  sugars  except 
lactose,  is  cleared  with  alumina  cream,  filtered,  boiled,  made  up  to 
an  appropriate  volume,  and  titrated  with  Fehling's  solution.  Ten  c.c. 
of  Fehling's  solution  =0-074  gramme  of  pure  lactose. 

Cane-Sugar. — A  portion  of  cold  water  extract  is  boiled  as  above 
with  2  per  cent,  citric  acid,  the  solution  neutralized,  and  titrated 
with  Fehling's  solution.     From  the  value  of  the  invert  sugar  so 


2oS  PRACTICAL  SANITARY  SCIENCE 

obtained  is  subtracted  the  dextrose  already  found;  the  difference 
reduced  by  5  per  cent,  (hydration  correction)  is  the  percentage  of 
cane-sugar. 

Fat. — Fat  of  dried  milks.  Owing  to  the  inclusion  of  fat  globules 
amongst  dried  proteins  the  solvent  action  of  ether  in  the  Soxhlet 
method  may  be  greatly  inhibited.  The  Werner- Schmidt  method 
is  in  this  case  more  suitable. 

Proteins. — The  N  is  determined  in  0-5  gramme  of  the  food  by 
Kjeldahl's  method,  and  the  figure  x  6-25. 

Water. — Five  grammes  are  dried  on  a  water-bath  (five  hours  or 
longer)  to  constant  weight. 

Ash. — Five  grammes  are  burnt  at  a  dull  red  heat  in  a  muffle. 
If  the  food  bums  with  difficulty,  H.2S04may  be  added,  and  a  correc- 
tion made  by  deducting  one-tenth  of  the  weight  of  the  ash. 

Cellulose  (material  insoluble  in  boiling*  water  and  not 
attacked  by  diastase). — To  5  grammes  of  the  food  freed  from 
fat  by  ether  if  necessary  add  200  c.c.  distilled  water,  and  bring  to 
the  boil.  Continue  the  boiling  for  half  an  hour.  Add  some  cold 
extract  of  malt  (15  to  25  c.c.  according  to  degree  of  activity),  and 
digest  at  55°  to  60'^  for  three  or  four  hours.  Filter  through  a  dry 
tared  filter.  Wash  the  residue  repeatedly  with  water  at  60°  C.  until 
free  from  all  reducing  sugar;  then  with  alcohol  and  ether.  Dry  for 
several  hours  on  water-oven  and  weigh.  Transfer  filter-paper  and 
residue  to  a  Kjeldahl  flask,  and  determine  the  protein.  Carry  out 
the  procedure  in  duplicate,  but  in  the  second  estimation  determine 
the  ash  instead  of  the  protein . 

The  first  weight  less  the  protein  and  ash  =  cellulose. 

Saccharifying"  Diastase. — Two  or  three  c.c.  of  a  5  per  cent,  cold- 
water  extract  of  the  food  are  allowed  to  act  for  an  hour  at  21°  on 
100  c.c.  of  a  2  per  cent,  soluble  starch  solution.  At  the  end  of  the 
hour  the  action  is  stopped  by  the  addition  of  10  c.c.  /^y  NaOH,  and 
the  whole  made  up  to  200  c.c.  The  amount  of  maltose  present  is 
determined  by  Fehling's  solution.  A  food  may  be  regarded  as 
having  a  diastatic  activity  of  100  when  0-2  c.c.  of  the  5  per  cent, 
solution  produces  under  these  conditions  sufficient  maltose 
(o-o8  gramme)  to  reduce  completely  10  c.c.  Fehling's  solution. 
If  double  the  amount  is  required,  the  diastatic  power  is  50,  etc. 


CEREALS  209 


CEREALS. 


The  composition  of  a  few  common  cereals  is  given  in  the  following 
table : 


Wheat 

Barley 

Rye 

Oats 

Maise 

Millet 

Rice 


Protein,  Fat.  J^f^^'  Cellulose,  Water.  Ash. 
nyclrates. 

II-O  1-7  71-2  2-2  12-0  1-9 

lo-i  1-9  69-5  3-8  12-3  2-4 

I0'2  2-3  72-3  2-1  II-O  2-1 

ii-o  5-2  57-3  12-0  II-8  27 

9-9  5-4  68-9  2-2  12-3  1-3 

10-4  3-9  68-3  2-9  12-3  2-2 

6-8  1-6  68-1  9-0  10-5  4-0 


It  will  be  seen  that  the  proteins  vary  somewhat  in  amount  in 
the  different  cereals.  The  fat  appears  in  increased  quantities  in 
those  cereals  which  grow  in  high  latitudes.  The  chief  carbohydrate 
is  starch:  it  forms  65  to  70  per  cent,  of  the  whole  grain.  The 
ash  averages  about  2  per  cent.,  and  is  composed  principally  of  lime 
and  phosphoric  acid,  thus  resembling  the  ash  of  animal  foodstuffs 
much  more  than  that  of  vegetables.  The  high  percentage  of 
carbohydrates  is  an  indication  that  cereals  should  be  mixed  with 
other  foods  richer  in  proteins  and  fat;  this  physiological  require- 
ment we  find  almost  universally  complied  with:  butter  is  spread 
upon  bread,  and  the  mixture  eaten  with  cheese.  On  the  whole, 
cooked  cereals  are  easily  digested  and  absorbed. 

Wheat-FlouP. — ^Wheat  is  the  most  important  cereal  used  in 
this  country.  It  is  consumed  to  the  extent  of  six  bushels  per  head 
per  annum.  The  grain  of  wheat  consists  of  three  portions:  (i)  The 
bran  or  outer  envelope  of  cellulose,  containing  mineral  matter, 
and  forming  13-5  per  cent,  of  the  grain;  (2)  the  endosperm,  con- 
stituting 85  per  cent,  of  the  whole,  and  consisting  of  nutritive 
material  for  the  growth  of  the  embryo;  (3)  the  embryo  or  young 
plant,  forming  1-5  per  cent,  of  the  grain.  The  bran  consists  of 
an  outer  layer  of  fibres  of  cellulose  impregnated  with  salts,  a  middle 
layer  of  pigment  cells,  and  an  inner  layer  of  aleurone  grains.  The 
endosperm  consists  of  a  delicate  reticulum  of  cellulose,  in  whose 
meshes  are  found  numerous  starch  granules.  The  embryo  is  com- 
posed of  small  cells  rich  in  protein  and  fat. 

The  milled  grain  known  as  flour  differs  in  composition,  according 

14 


2IO 


PRACTICAL  SANITARY  SCIENCE 


to  whether  the  bran  or  embrj-o,  or  both,  have  been  largely  removed 
or  retained.  The  reduction  of  bran  to  a  powder  by  grinding  is  a 
difficult  and  expensive  matter,  and  as  a  rule  the  miller  removes  it 
altogether.  In  roller-milling,  the  germ  is  also  removed,  in  order 
to  prevent  the  fat  which  it  contains  becoming  rancid.  Enzymes 
present  in  the  germ  act  upon  the  starch,  converting  it  into  dextrin 
and  sugar,  which  darken  the  colour  of  the  bread;  so  the  genu  is 
excluded.  This  rejection  of  the  bran  and  germ  means  the  loss  of 
some  of  the  most  useful  constituents  of  the  wheat;  and  the  recog- 
nition of  this  loss  has  led  to  a  number  of  patent  processes  for  treating 
the  bran  and  germ  so  as  to  prevent  the  production  of  a  dark  loaf. 
In  the  '  Hovis  '  process,  the  fat  of  the  genu  is  treated  with  steam, 
with  the  object  of  preventing  its  becoming  rancid.  In  the  '  Frame 
Food  '  process,  the  bran  is  boiled  with  water  under  pressure,  with 
the  object  of  breaking  do^^^l  the  cellulose,  and  extracting  the  bulk 
of  the  nitrogenous  and  mineral  constituents.  In  Smith's  patent 
the  genu  is  partiallj^  cooked  by  superheated  steam,  whereby  the 
ferment  is  killed  which  transforms  the  starch  of  the  flour.  Accord- 
ing to  the  method  adopted  in  milling,  some  flours  contain  more  bran 
than  others,  and  some  more  starches  and  gluten. 

Wheat  from  different  countries  varies  in  chemical  composition. 
Ordinary  bread  is  made  from  a  mixture  of  flours  derived  from 
different  wheats,  and  sometimes  such  a  mixture  includes  different 
types  of  milling. 

The  average  composition  of  wheat-flour  is: 


Water 

•  •     13-0 

Sugar 
Ash 

..       07 
..       0-8 

Fat 

•       1-5 

Protein 

. .       II-O 

Starch, 

dextrin,  and  cellulose     . . 

•  •     73-0 

Physical  Characters  of  Flour. — Flour  should  be  free  from  acidity, 
white  in  colour,  and  smooth  when  rubbed  between  the  fingers.  It 
should  be  entirely  free  from  fungi  and  all  other  parasites.  A  yellow 
colour  denotes  age  or  femientation.  If  flour  be  kept  in  a  damp 
place,  an  odour  is  generated  by  the  growth  of  moulds  and  various 
micro-organisms. 

Gluten. — The  crude  protein  of  flour  known  as  gluten  possesses 


CEREALS  211 

a  constituent,  gliadin,  which  confers  upon  dough  its  characteristic 
adhesiveness.  When  dough  is  thoroughly  washed  so  as  to  get  rid 
of  starch  and  all  other  soluble  bodies,  such  as  salts,  albumin,  sugar, 
etc.,  gluten  remains  as  a  somewhat  tough  and  sticky  mass;  when 
this  is  blown  up  with  a  gas,  it  coheres  sufficiently  to  remain  in  the 
form  of  a  sponge.  Barley,  rice,  and  oatmeal  do  not  contain  gluten, 
but  other  forms  of  protein,  which  are  destitute  of  this  viscid  char- 
acter; hence  they  cannot  be  made  into  bread  unless  mixed  with  a 
sufficient  quantity  of  wheat-flour. 

Estimation  of  Gluten. — Place  20  grammes  of  flour  in  a  basin 
and  stir  it  into  a  stiff  dough  with  warm  water ;  next  thoroughly 
work  the  dough  with  the  fingers  in  a  fine  muslin  bag  in  a  stream 
of  running  water  until  all  the  starch  and  other  soluble  materials 
have  been  washed  away.  The  absence  of  starch  may  be  proved  by 
the  iodine  test.  Generally  a  small  quantity  of  fats  and  salts 
(i  per  cent.)  remains.  Now  spread  out  the  gluten  in  a  weighed  dish 
in  a  water-oven;  dry  until  a  constant  weight  is  obtained.  This 
weight,  minus  the  weight  of  the  dish,  represents  the  gluten. 

A  more  delicate  and  reliable  method  is  the  estimation  of  total 
nitrogen  by  Kjeldahl's  process,  as  described  previously.  The  total 
N  X  6-3  gives  approximately  the  gluten.  In  carrying  out  the  process 
great  care  should  be  taken  that  no  ammonia  and  no  nitrates  exist 
in  the  reagents  used.  If  the  gluten  fall  below  8  per  cent.,  the  flour 
may  be  regarded  as  not  pure  wheat-flour. 

Ash. — The  ash  of  wheat-flour  consists  principally  of  phosphates 
of  potassium,  magnesium,  and  calcium,  together  with  mixed  salts 
of  sodium  and  iron,  and  lastly  silica.  The  total  quantity  should 
not  much  exceed  i  per  cent.  The  estimation  should  be  done  in  a 
platinum  basin,  and  a  wholly  white  ash  obtained.  Ash  amounting 
to  2  per  cent,  shows  the  addition  of  mineral  adulterants. 

Water. — This  constituent  should  not  exceed  16  per  cent.  The 
adulteration  of  wheat-flour  at  present  consists  essentially  in  the 
addition  of  other  flours,  as  those  of  rice,  maize,  pea,  and  bean. 
The  microscopic  appearances  of  the  different  starch  granules  will 
assist  in  the  detection  of  such  adulterations. 

Starch  Granules. — To  estimate  the  amount  of  starch  in  a  sub- 
stance, weigh  out  a  gramme  of  the  dried  powdered  material,  and 
mix  it  with  50  c.c.  of  a  5  per  cent.  HCl  solution  in  a  flask,  to  which  a 


212  PRACTICAL  SAMTARY  SCIE.XCE 

reflex  condenser  is  attached ;  boil  for  several  hours  under  a  hood : 
the  starch  is  converted  into  sugar  (dextrose).  Make  the  solution 
slightly  alkaline  with  NaOH  solution,  and  estimate  the  dextrose 
by  Fehling's  method.  The  result,  multiplied  by  0-9,  gives  the 
quantity  of  starch  in  a  gramme.  Where  cellulose  is  present,  the 
small  amount  converted  into  sugar  may  be  ignored.  The  micro- 
scopic appearances  of  manj'  starch  granules  are  such  as  to  afford 
an  easy  means  of  recognition.  If  a  mere  speck  of  a  particular 
flour  or  powdered  starch  be  placed  on  a  microscopic  slide,  a  drop 
of  water  added,  and  a  cover-slip  applied,  the  starch  granules  can  be 
thoroughly  studied  by  low  and  high  powers  of  the  microscope. 
As  in  mounting  specimens  of  bacteria,  it  should  be  noted  that  it 
is  almost  impossible  to  apply  too  little  of  the  material  to  the  slide. 
The  student  should  observe  that  in  most  cases  characteristic  cells 
appear,  but  that  many  cells  may  be  unrecognizable,  as  belonging 
to  any  particular  kind  of  starch.  Where  starch  granules  of  different 
foodstuffs  closely  resemble  each  other,  it  may  be  quite  impossible 
to  decide  whether  or  not  slight  admixture  has  been  effected.  On 
the  other  hand,  when  the  granules  are  dissimilar  the  slightest 
admixture  is  easily  detected. 

If  an  estimation  of  the  amount  of  the  adulteration  be  required, 
a  rough  average  percentage  of  the  foreign  granules  may  be  obtained 
by  counting  a  number  of  fields,  and  this  estimation  may  be  checked 
by  making  a  mixture  containing  the  true  and  foreign  ingredients 
in  the  proportions  observed;  such  mixture  should  present  the 
same  microscopic  appearances  as  the  original.  Several  trials  may 
be  made  in  this  way  before  the  required  match  is  obtained.  The 
student  should  carefully  study  the  microscopic  characters  of  all 
starch  granules  occurring  in  vegetable  foods,  and  make  drawings 
of  them. 

Bleaching-  of  Flour  and  Flour-Imppovers.— With  a  view  to 
improving  the  baking  qualities  of  flour,  millers  resort  to  bleaching 
and  the  addition  of  '  improvers.'  Ozone,  halogens,  and  nitrogen 
peroxide  have  been  used  as  bleaching  agents.  Nitrogen  peroxide 
alone  appears  to  give  satisfactory  results,  and  is  the  only  bleacher 
now  used.  The  gas  is  produced  chemically  from  nitric  acid  and 
ferrous  sulphate,  or  electrically  by  the  combination  of  the  N  and 
O  of  the  air  by  an  electrical  sparking  discharge.     The  latter  is  said 


CEREALS  213 

to  be  the  better  method  in  that  the  degree  of  bleaching  is  more 
easily  controlled,  and  condensation  of  acid  resulting  in  staining  of 
the  flour  less  likely  to  occur.  Air  charged  with  nitrogen  peroxide 
and  ozone  is  agitated  with  the  flour  in  a  suitable  machine.  It  is 
stated  that  the  nitrogen  peroxide  produced  by  3  c.c.  of  nitric  oxide 
in  3  litres  of  air  will  bleach  i  kilogramme  of  flour. 

A  watery  extract  of  bleached  flour  reacts  to  the  nitrite  test  of 
Griess.     This  reaction  is  not  given  by  ordinary  unbleached  flour. 

When  bleached  flour  is  baked,  one-half  to  two-thirds  of  the  nitrite 
disappears,  and  an  increase  in  nitrates  occurs.  The  whole  of  the 
nitrite  may  disappear  from  biscuits. 

Effects  of  Bleaching. — Bleaching  destroys  the  yellow  colouring- 
matter  dissolved  in  a  thin  layer  of  oil  which  surrounds  the  individual 
granules  of  starch;  the  iodine  value  of  this  oil  is  lowered.  The  acidity 
of  flour  is  increased.  It  is  probable  that  certain  amino-groups  in 
the  protein  are  destroyed. 

Improvers  used. — Water  added  to  the  flour  in  a  fine  spray;  phos- 
phates, especially  calcium  phosphate;  phosphoric  acid;  sulphury] 
chloride.  It  has  been  experimentally  shown  that  even  traces  of 
nitrites  in  flour  inhibit  both  proteolytic  and  amylolytic  digestion. 

The  introduction  of  roller-milling  made  it  possible  to  utilize  any 
variety  of  wheat  since  pulverization  of  the  bran  is  avoided,  and 
consequently  a  more  complete  removal  of  bran  and  germ  effected. 

The  germ  contains  no  gliadin  nor  glutenin  (these  substances  unite 
with  water  to  form  gluten);  it  contains  10  per  cent,  of  albumin, 
5  per  cent,  of  globulin,  and  3  per  cent,  of  proteose.  Its  nucleated 
cells  contain  a  considerable  amount  of  nucleic  acid  combined  with 
albumin  and  globulin.  Little  organic  phosphorus  accordingly  occurs 
in  the  endosperm.  Wheat  contains  probably  about  2  per  cent,  of 
germ,  and  as  the  latter  possesses  at  least  30  per  cent,  of  proteins, 
retention  of  the  germ  raises  the  protein  content  of  flour  by  o-6  per 
cent. 

The  greater  portion  of  the  phosphorus  in  bran  can  be  extracted 
with  dilute  acid,  and  it  has  been  shown  that  the  bulk  of  this  phos- 
phorus occurs  in  organic  combination  as  a  phospho-organic  acid, 
combined  with  potassium,  calcium,  and  magnesium. 

Wholemeal  or  Graham  flour  is  produced  by  grinding  the  entire 
wheat  grain;  it  should  contain  the  whole  of  the  germ. 


214  PRACTICAL  SAXITARY  SCIENCE 

'  Entire  '  wheat  flour  or  line  meal  is  obtained  by  removing  a 
portion  of  the  bran,  and  finely  grinding  the  rest;  it  contains  a 
portion  of  the  germ. 

'  Straight-rmi '  flour  is  the  whole  of  the  flour  produced  in  the 
roller-mill.  The  percentage  composition  of  bread  made  from 
samples  of  these  flours  is  as  follows: 


Protein 
(NX  5-7). 

Carbo- 
hydrates. 

Fats. 

Water. 

Ash. 

Graham  flour 

•  •     9-54 

46-10 

0-29 

42-68 

1-39 

'  Entire  '     . . 

•  •     Q-32 

4875 

0-19 

40-97 

0-77 

'  Straight  run  ' 

•  •     0-63 

51-06 

0-04 

3877 

0-50 

Experiments  have  been  made  on  the  nutritional  values  of  different 
varieties  of  flours.  Young  rats  have  been  fed  on  '  standard '  or 
'  straight  run,'  and  others  of  the  same  age  on  '  entire.'  The  first  lot 
throve  much  better  than  the  second.  Again,  the  same  experiment 
has  been  carried  out  with  Graham  flour  and  '  entire,'  or  white  flour, 
with  results  in  favour  of  the  Graham  variety. 

In  the  milling  of  rice  the  cuticle,  consisting  of  pericarp,  testa, 
and  nucellus,  is  frequently  removed.  A  diet  consisting  exclusively 
of  such  rice  produces  polyneuritis  and  other  changes,  constituting 
a  disease  known  as  '  beri-beri.'  If  the  offal  (about  10  per  cent,  of 
the  grain)  be  returned  to  the  rice,  no  beri-beri  occurs.  Or  if  the 
offal  be  extracted  by  0-3  per  cent.  HCl  and  the  extract  precipitated 
by  proof  spirit,  the  substances  soluble  in  alcohol  (1-6  per  cent,  of  the 
grain)  will  equally  prevent  the  disease.  It  is  significant  that  the 
precipitate  containing  85  per  cent,  of  the  phosphorus  of  the  offal  is 
wholly  ineffective  in  preventing  the  disease.  A  good  rice  should 
not  contain  less  than  0-4  to  0-5  per  cent,  total  phosphorus.  The 
milling  of  rice  deprives  it  of  its  cuticle,  and  leaves  it  with  a  dull 
appearance.  To  improve  its  appearance  it  is  '  polished  '  in  hollow 
cylinders  fitted  with  revolving  rollers  covered  with  sheep-skin.  In 
order  to  obtain  a  high  polish  talc  or  steatite,  in  the  form  of  a  fine 
powder,  is  added  to  the  rice  prior  to  polishing,  and  for  the  most  part 
as  it  passes  through  the  mill.  Gypsum,  kaolin,  and  gums  have  been 
also  used  for  this  purpose.  The  colour  of  rice  is  changed  from  a 
cream  to  a  dead  white  by  the  addition  of  blue  pigments  (generally 
ultramarine)  during  milling,  and  to  make  it  transparent  it  is  treated 
with  arachis  and  other  oils. 


CEREALS 


2i5 


I.  Granules  of  Wheat,  Barley,  and  Rye— t^/j^a^— These  are 
(i)  large,  round,  or  oval,  which  do  not  exhibit  concentric  striae; 

n 


©4    ^}u  -^^ 


-  'O 


m 


Q 

Fig.  29. — Wheat,     x  200. 


J 


^^ 


Fig.   ^o. — Barley,     x  200 


■   ^ 


'^,.' 


(2)  small,  ill-defined  granules  scattered  irregularly  throughout  the 
field.     Intermediate  sizes  are  rare. 


2l6 


PRACTICAL  SAXITARY  SCIENCE 


Barley. — These  are  (i)  large,  (2)  small,  (3)  intermediate  in  size, 
In  a  very  few  are  there  any  markings. 


o    Q    ._^.  ' 


Fig.    :ti. — Rye.      x  200. 


il 


Fig,  32. — Rice,     x  200. 

Rye. — ^These  are  very  similar  to  those  of  barley,  except  that  in 
the  large  granules  some  show  a  rayed  hilum  and  cracked  edges; 


CEREALS  217 

the  large  granules  are  more  generally  circular  and  flattened  than 
those  of  wheat  and  barley,  and  somewhat  larger. 


_.,^A)^.«,^,.^ 


4?-   t' 


_*3-c,.''^     '  '■  ^.".^ '^^V5^ 


Fic 

'•  33-- 

-Oat.     X  200. 

' 

00 

Cs 

v^  ■ 

% 

... 

" 

0^ 

t)  ■ 

■fi 

't^ 

^<^^^ 

0 

OO' 

"k^* 

0 

®' 

0       .\ 

W 

0 

! 

P' 

3 

.0  • 

0 

;     0 

0       ^-^ 

^•(3 

0  V^  Q          - 

oO 

\  0 

0 

1     0 

0  .<? 
0  ° 

0 

^0 

9 

Fig.  34. — Maize,     x  200. 

2.  Rice,    Oatmeal,    and    Maize   exhibit  small   faceted   and 
angular  granules  destitute  of  concentric  markings.    The  granules 


211 


PRACTICAL  SAXITARY  SCIENCE 


of  rice  are  small,  and  collect  in  part  into  angular  masses.     Those 
of  oatmeal  are  slightly  larger,  and  collect  into  rounded  masses. 


"cQ 


.0 .     ^  ^ 


o 


Fig.  ^6. — -Tapioca,     x  200. 


Maize  granules  are  much  larger  and  more  irregular  in  shape,  and 
most  of  them  possess  a  stellate  hilum. 


CEREALS 


219 


3.  Sag-O    and    Tapioca— These  granules   are  irregular   in   out- 
line, being  angular  and  partially  rounded;  they  are  irregular  in 


Fig.  37. — Pea.     x  200. 


Fig.  38. — Haricot  Bean,     x  200. 

size,  and  mostly  possess  a  central  hilum ;  occasionally  thej''  exhibit 
concentric  strise.     Sago  granules  are  large  and  very  irregular  in 


220 


PRACTICAL  SAMTARY  SCIENCE 


shape — for   the  most  part  somewhat  rounded   at  one  side  and 
truncated  at  the  opposite;  the  hiluni  is  cither  stellate  or  linear. 


> 


O0 


0 


b 


"     '  0  0 


^.^^o-^ 


^' 


Fig.  39. — Arrowroot,     x  200. 


Fig.  40. — Potato,     x  200. 

Tapioca  granules  are  much  smaller,  and  the  hilum  is  generally 
placed  towards  the  rounded  extremity. 


CEREALS  221 

4.  Pea    and    Bean. — These    granules   are  oval    in    form,  fairly 

uniform  in  size,  and  possess  a  central  linear  liilum  and  faint  con- 
centric strise.      Those  of  the  pea  present  a  central  longitudinal 

hilum,  sometimes  exhibiting  cross-striation.  The   granules  of  the 

bean  are  somewhat  larger  and  broader,  and  the  cross-striation  of 
the  central  hilum  is  more  marked. 


V 


Fig.  41. — -Vibrio  Tritici.     x  30. 


Fig.  42. — Bruchus  Pisi. 


Fig.  43. — AcARUS  Farin.^. 


5.  ArroWFOOt  and  Potato. — The  granules  of  these  starches 
are  large,  pyriform,  and  marked  distinctly  with  concentric  strise. 
A  circular  hilum  is  found  in  both,  placed  at  the  large  extremity 
in  arrowroot,  and  at  the  small  in  potato.  The  granules  of  farrow- 
root  do  not  swell  in  a  solution  of  KOH,  as  do  those  of  the  potato. 


PRACTICAL  SAX  IT  A  RY  SCIENCE 


Parasites  found  in  Wheat  and  Flour— Animal:  Tylenchns 
tritici  (ear  cockle). — In  the  infected  ears  of  grain  are  to  be  seen  the 
larvje  of  a  nematode  wonn,  occurring  as  a  white  powder  in  dark 
misshapen    grains.      Specimens    may    be    mounted    directly    in 


Fig.  44. — Penicillium 
Glaucum. 


Fig.  45. — Aspergillus 
Glaucus. 


M 


^h 


Fig.  46. — MucoR  Mucedo. 

A,  Head ;  B  and  C,  conjugation; 
D,  spore-bearing  hyphse. 


Fig.  47. — Peronospora. 


Farrant's   solution,  or  dehydrated   and   cleared   in   the   ordinary 
manner,  and  mounted  in  Canada  balsam. 

Bruclms   pisi   and   Calandra   gran  aria   are   beetles   (Coleoptera) 
which  infest  grain  and  pulses.     The  first  attacks  the  pea,  an  allied 


CEREALS  223 

species  the  bean,  whilst  Calandra  is  found  in  grain.  The  female 
lays  her  eggs  in  the  young  fruit,  and  the  larvae  destroy  the  internal 
parts.  The  C.  granaria  perforates  the  husk  of  the  grain  and 
abstracts  the  contents. 

.  Acanis  Farince. — This  parasite  is  found  in  inferior  and  damp 
flour.  It  may  be  distinguished  from  the  A.  scabei  by  its  legs 
remaining  thick  up  to  their'  extremities,  whilst  in  the  itch  parasite 
the  distal  ends  of  the  legs  are  quite  thin. 

Veg-etable  Parasites  found  in  Wheat,  Flour,  Bread,  etc. 
— Moulds :     Penicilliiim    glaticum,     Aspergillus     glaucus,     Miicor 


^  © 


^O 


o 


Fig.  48. — UsTiLAGo  Segetum.     x  250. 

mucedo,  and  Peronospora. — These  moulds  are  easily  distinguished 
by  the  characters  of  the  ends  of  the  spore-bearing  hyphffi.  In 
penicillium  the  last  hypha  branches  into  three  or  four  temiinal 
filaments,  which  develop  round  or  oval  spores  in  rows  in  their 
long  axes.  In  aspergillus  the  end  of  the  spore-bearing  hypha 
enlarges,  and  from  this  pedicle-bearing  spores  grow  out  and  form 
a  more  or  less  dense  head.  In  mucor  the  end  of  the  spore-bearing 
hypha  enlarges  greatly,  and  the  spores,  instead  of  grow-ing  out 
from  the  enlargement,  as  in  aspergillus,  grow  inside  a  membrane 
which  surrounds  the  head.  When  the  spores  have  matured,  the 
membrane  ruptures  and  sets  them  free. 


224  PRACTICAL  SAXITARY  SCIENCE 

Peronospora,  which  caused  the  Irish  potato  famine  of  1847,  first 
affects  the  leaves,  then  travels  down  the  stem,  and  finally  attacks 
the  tubers.  The  spore-bearing  hyphae  branch  and  rebranch,  and 
at  the  end  of  a  terminal  branch  a  single  spore  is  developed. 

Ustilago  Segeiiim  (smut). — The  spores  of  this  parasite  are  found 
as  a  black  powder  infesting  ill-developed  cars  of  com,  and  fall  off 
when  the  ear  is  rubbed.  Examined  microscopically,  they  are  seen 
to  be  brown,  spherical,  free  spores. 


t 


Fig.  49. — TiLLETiA  Caries  (Uredo  Fcetida).     x  250. 

Tilletia  caries  (bunt)  is  another  member  of  the  ustilaginse,  and 
is  found  in  the  interior  of  the  grain;  it  may  escape  detection  until 
the  process  of  milling  takes  place.  The  spores  are  brov^Ti,  spherical 
bodies,  generally  free,  and  give  to  the  interior  of  the  affected  grain 
a  sooty  appearance  and  foetid  odour.  These  spores  germinate 
in  the  spring,  forming  a  hypha,  the  promycelium,  which  bears 
promycelial  thread-like  spores.  The  next  stage  in  the  life-history 
of  this  organism  is  the  conjugation  of  contiguous  spores.  Two 
such  conjugated  spores   bud  and  form   an   elongated  secondary 


CERE A LS 


225 


promycclial  spore,  which,  if  it  find  a  suitaV^lc  host,  sends  out  hyphie 
and  enters  the  interior  of  the  grain,  where  a  myceHum  is  developed. 
After  a  time  the  hyphic  swell,  become  dark  in  colour,  and  a  differ- 
entiation into  spores  takes  place.  As  these  ripen,  the  mycelial 
structure  disappears,  and  leaves  the  resting  spores  in  the  condition 
from  which  the  cycle  commenced. 

Pticcinia  graminis  is  one  of  a  large  number  of  parasitic  species 
affecting  corn  in  the  manner  above  described.  A  spore  attaches 
itself  to  a  grain  or  stem,  and  sends  hyphge  into  its  substance,  from 


Fig.  50. — Wheat  Stem  infected  with  Puccinia. 

which  a  mycelium  and  spores  are  formed  within;  as  a  result,  the 
grain  ruptures,  and  the  spores  appear  on  the  surface  as  rust.  A 
distinctive  feature  of  puccinia  is  the  double  spore  attached  to  a 
peduncle.  It  is  this  form  which  is  found  attached  to  grain  or  grass 
in  the  autumn,  as  rust,  and  which,  known  by  the  name  teleuto- 
spore,  remains  quiescent  during  winter.  In  spring  it  germinates, 
and  produces  a  non-parasitic  mycelium.  The  individual  cells  of 
this  mycelium  produce  filaments,  known  as  gonidiophores,  which 
in  turn  produce  spores  at  their  free  ends.  Distributed  by  the 
wind,  these  latter  fall  on  the  leaves  of  the  barberr}',  where  they 


226 


PRACTICAL  SANITARY  SCIENCE 


germinate  and  form  a  dense  mycelium  in  the  substance  of  the  leaf, 
giving  rise  to  swellings  which  project  on  its  under-surface.    Spherical 


Fig.  51. — Portion  of  Fig.   50  slightly 
MORE  Highly  ^Magnified. 


Fig.  52. — Teleutospores 


Fig.  53. — .lEciDiuM  Berberidis.        Fig.  54. — Gonidiospores  (Uredo 

gonidia)  and  Teleutospore. 


structures,   termed    ascidia,    form    and   develop  within  themselves 
spores  which  are  set  free  on  rupture  of  the  wall  of  the  aecidium. 


CEREALS 


227 


These  spores  are  carried  by  the  wind  to  grass  plants,  to  which 
they  attach  themselves  and  develop  a  mycelium  from  which  grow 
certain  hyphse,  bearing  single  spores  (uredogonidia).  On  rupture 
of  the  leaf  of  the  host,  the  spores  arc  to  be  seen  as  a  yellow  dust. 
Again  the  wind  carries  the  gonidium  to  another  grass,  where  it 
germinates,  produces  hyphse,  and  repeats  the  previous  process 
(uredo  form).  As  the  autumn  approaches,  special  hyphse  produce 
gonidia,  which  have  a  septum  perpendicular  to  the  long  axis, 
dividing   the    spore  into   two    cells — the   teleutospore ;    this    rests 


Fig.  55. — Ergot  in  Rye.     x  30. 

through  the  winter,  and  commences  the  cycle  once   more   in   the 
following  spring. 

Claviceps  purpurea  (ergot)  grows  in  rye,  and  the  mycelial  growth 
(sclerotium)  replaces  the  grain.  The  ergot  masses  (or  grains)  are 
larger  than  the  rye-grains,  and  of  a  deep  purple  colour.  In  the 
spring  the  sclerotium,  which  has  rested  through  the  winter,  ger- 
minates, and  produces  long  hyphse  (stromata),  which  develop  a 
swelling  at  the  distal  end,  which  latter  contains  oval  receptacles 
(ascocarps).  Attached  to  the  inner  end  of  the  ascocarps  are  asci, 
containing    eight  filiform   spores   (ascospores).     The   asci  rupture 


228 


PRACTICAL  SAXITARY  SCIENCE 


and  the  spores  escape.  Carried  bj'  the  wind,  the  spores  alight  on 
the  ovarj'  of  the  rye  liower  and  form  a  niycehuni.  On  the  surface 
of  this  mycehum  free  spores  (gonidia)  develop,  and  are  surrounded 
by  a  viscid  substance,  known  as  honey-dew,  which  attracts  insects, 


% 


:>"' 


Fig.  56. — ScLEROTiuM  bearing 
Stromata.      X  I. 


Fig.  57.— Strojia  containing 
ascocarps.      x  75 


by  which  the  spores  are  carried  to  other  flowers,  where  the  process 
is  repeated.     This  stage  is  known  as  the  sphacelia  form. 

As  the  rye  is  developed,  the  mycelial  growth  increases  to  such 


Fig. 


58. — AscocARP  containing 
Asci.     X  350. 


Fig.  59. — Ascus  containing 

ASCOSPORES. 


an  extent  that  the  young  grain  is  wholly  absorbed,  the  pericarp  is 
no  longer  able  to  contain  it,  and  it  projects  like  a  spur  from  the 
spike.  Ultimately  it  falls  to  the  ground.  The  cycle  is  repeated  in 
the  following  spring. 


BREAD 


229 


The  seeds  of  Lolinm  ienmlentum,  possessing  nareotic  properties, 
may  gain  access  to  flour,  l)ut  rarely  produce  poisoning. 


BREAD 

Bread  is  chiefly  made  from  wheat-flour.  A  dough  is  first  formed 
by  mixing  the  flour  with  water  or  other  fluid,  and  a  gas,  generally 
CO2,  is  passed  through  it.  Carbon  dioxide  is  obtained  cither  by 
tlie  action  of  yeast  on  sugar,  when  this  gas  and  alcohol  are  formed, 
or  through  the  liberation  of  the  gas  from  an  alkaline  bicarbonate 
by  the  action  of  an  organic  acid.  The  dough  is  sometimes  aerated 
by  charging  water  with  air  and  mixing  this  with  flour  under  pressure 
in  air-tight  chambers ;  afterwards  the  pressure  is  lowered  by  opening 
a  trap,  when  the  dough  is  blown  up  by  the  expanding  gas,  forming 
'  aerated  '  bread.  The  dough  is  then  cooked  in  an  oven  at  a  tem- 
perature of  200-205°  C. 


Composition  of  White  Bread : 

Water 

Proteins 

Fat 

Starch,  sugar,  dextrin 

Cellulose     . . 

Ash 

Composition  of  Whole  Meal : 

Water 

Proteins 

Fat 

Starch,  sugar,  dextrin 

Cellulose 

Ash  ..  .. 


40-0 

6-5 
i-o 

51-2 

0-3 

T-O 


45-0 
6-3 

1-2 

44-8 
1-5 

1-2 


During  the  cooking  a  crust  is  formed,  which  should  neither  be 
very  light  nor  very  dark  in  colour,  and  which  should  crack  readily 
on  breaking.  The  shining  appearance  of  crust  is  due  to  the  for- 
mation of  dextrin,  and  its  flavour  and  dark  colour  to  the  production 
of  caramel.  Two-thirds  of  the  volume  of  a  good  loaf  is  gas.  Great 
whiteness  in  a  loaf,  although  much  desired  by  the  public,  is  by  no 
means  essential  from  a  nutritive  point  of  view,  as  a  very  white  loaf 
possesses  a  maximum  of  starch  and  a  minimum  of  protein. 


2  3') 


PRACTICAL  SAXITARY  SCIEXCE 


Comparative  Composition  of  Crust  and  Crumb : 

Crust.  Crumb. 


Water          

••     17-15 

44-45 

Insoluble  protein   . . 

•  •       7-30 

5-92 

Soluble  protein 

■  •       570 

075 

Dextrin  and  sugar  . . 

. .       4-88 

3-79 

Starch 

..     62-58 

43-55 

Fat 

..       i-i8 

070 

Ash 

I-2I 

0-84 

By  these  figures  it  is  seen  that  there  is  a  much  larger  proportion 
of  solids,  and  also  more  soluble  proteins  and  carbohj'drates,  in  the 
crust  than  in  the  crumb.  The  crumb  should  be  elastic  in  con- 
sistence, should  have  a  sweet,  nutty  flavour,  and  be  of  a  uniform 
whiteness  throughout.  As  bread  grows  old,  it  becomes  hard,  and 
it  has  long  been  known  that  reheating  softens  it.  The  real  explana- 
tion of  the  staling  of  bread  does  not  seem  to  be  known.  Bibra 
holds  that  in  fresh  bread  there  is  free  water  present,  which,  as 
staleness  supervenes,  unites  with  starch  or  gluten,  and  that  re- 
heating sets  this  water  free.  He  states  that  the  freshness  will 
not  return  if  the  bread  has  lost  30  per  cent,  of  its  water.  Others 
hold  that  the  stale  condition  is  produced  by  the  shrinkage  which 
takes  place  in  the  fibres  forming  the  walls  of  the  pores.  The  water 
vapour  formed  by  the  second  heating  drives  these  fibres  apart  again. 
It  should  be  noted  that  during  the  baking  of  bread  a  large  pro- 
portion of  the  fat  is  lost,  amounting  to  as  much  as  7  per  cent,  in 
some  instances,  that  the  proteins  are  diminished  from  i  to  2  per 
cent.,  and  the  carbohydrates  from  3  to  4  per  cent.  Some  of  the 
starch  is  converted  into  soluble  starch  and  dextrin  to  the  extent 
of  8  per  cent. 

The  estimation  of  Water  and  Mineral  Matter  in  bread  is  per- 
formed as  in  the  case  of  flour.  Twenty  grammes  of  the  crumb 
make  a  convenient  quantit}^  with  which  to  work. 

The  Ash  is  generally  greater  in  weight  than  that  of  the  flour  used, 
owing  to  the  sodium  chloride,  baking-powder,  etc.,  added.  Any 
excess  of  ash  above  3  per  cent,  is  generally  regarded  as  due  to  salts 
added  in  order  to  improve  the  colour. 

Silica  is  estimated  by  treating  the  ash  with  strong  HCl  and  hot 
distilled  water  in  a  platinum  dish,  then  filtering  through  a  Swedish 
filter-paper,  carefully  washing  the  platinum  dish  with  further  boil- 


BREAD  231 

ing  distilled  water,  and  transferring  the  washings  to  the  lilter-papcr. 
When  the  residue  on  the  filter  has  been  several  times  washed  with 
boiling  distilled  water  so  that  all  soluble  substances  have  passed 
through,  it  is  dried  in  a  water  oven,  transferred  to  a  porcelain 
crucible,  ignited,  and  weighed  as  silica.  It  should  not  exceed 
2  per  cent. 

Acidity. — Soak  5  grammes  of  bread  in  50  c.c.  of  water  for  an 
hour.  Filter  and  titrate  the  filtrate  with  y^  NaOH,  using  phenol - 
phthalein  as  indicator.  The  number  of  c.c.  of  decinormal  soda 
used  multiplied  by  6  equals  milligrammes  of  glacial  acetic  acid 
in  5  grammes  of  bread.  The  acidity  should  not  exceed  o-il  per 
cent. 

Adulteration. — Formerly  Alum  was  used  to  whiten  inferior 
flours,  but  at  present  it  is  practically  never  found.  The  detection 
of  alum  in  bread  is  carried  out  as  follows :  Dissolve  a  small  quantity 
of  haematoxylin  in  alcohol,  and  to  this  add  a  little  freshly  prepared 
solution  of  ammonium  carbonate  in  distilled  water.  Cubes  of 
crumb  are  cut  from  the  centre  of  a  loaf,  and  small  quantities  of 
the  solution  poured  upon  them,  after  which  they  are  removed  to 
a  water  oven  and  dried  at  a  low  temperature.  The  production  of 
a  permanent  lavender  colour  denotes  the  presence  of  alum.  To 
a  small  degree  magnesium  salts  simulate  alum  in  this  reaction,  but 
the  colour  on  drying  is  not  so  permanent.  Silicate  of  alumina 
exists  normally  in  flour,  but  in  such  small  quantities  that  a  4-pound 
loaf  will  not  contain  more  than  6  or  7  grains.  The  part  played  by 
alum  when  added  to  inferior  flours  is  that  of  checking  fermentation, 
which  otherwise  would  lead  to  the  production  of  glucose,  and  con- 
sequently a  discoloured  bread.  It  is  stated  that  alum  increases 
the  porosity  of  bread.  This  adulterant  has  been  found  in  quantities 
ranging  from  20  grains  to  100  grains  per  4-pound  loaf. 

Quantitative  Estimation. — Reduce  ^  pound  of  the  bread  to  ash, 
and  separate  off  the  silica  on  a  filter  by  treatment  with  strong 
HCl  and  boiling  water  in  the  usual  manner.  The  filtrate  contains 
phosphates  of  lime  and  magnesia,  iron,  and  aluminium.  To  this 
solution  add  5  c.c.  of  (NH4)H0,  which  will  precipitate  all  the 
phosphates,  and  20  c.c.  of  strong  acetic  acid,  which  redissolves  the 
phosphates  of  lime  and  magnesia.  Filter  and  wash  the  residue 
of  phosphates  of  iron  and  aluminium  with  boiling  water.     Dry, 


232  PRACTICAL  SAXITARY  SCIENCE 

ignite,  and  weigli.  The  residue  is  now  dissolved  in  strong  HCl, 
and  diluted  to  200  c.c,  and  the  iron  estimated  colorimetrically. 
Convert  the  iron  thus  found  into  ferric  phosphate  by  multiplying 
by  2-7,  and  subtract  this  from  the  weight  of  phosphates  of  iron  anil 
aluminium  previously  obtained;  deduct  also  the  weight  of  the 
filter  ash,  and  the  difference  is  aluminium  phosphate,  which  may 
be  returned  as  commercial  alum  (crystallized  ammonium  alum)  by 
multiplying  by  37. 

Various  cereal  and  casein  preparations  have  appeared  in  recent 
years  containing  added  Phosphorus  Compounds  in  different 
forms — glycerophosphates,  lecithins,  and  lipolins,  etc.  In  order  to 
measure  these  added  substances  it  is  necessary  to  estimate  the 
phosphorus.     This  is  easily  effected  by  Neumann's  method: 

Prepare  2  litres  of  Neumann's  molybdate-nitrate  solution;  dis- 
solve 75  grammes  of  ammonium  molybdate  in  500  c.c.  of  water,  and 
pour  this  into  500  c.c.  HNO3;  add  a  litre  of  50  per  cent,  ammonium 
nitrate  solution. 

Prepare  mashed  hlter-paper  for  pressure  filter.  Place  30  grammes 
of  minced  filter-paper  in  a  litre  of  water  containing  50  c.c.  HCl. 
Heat  on  water-bath  with  shaking  for  an  hour.  Filter.  Wash  with 
water  repeatedly  till  all  acid  disappears.  Leave  in  2  litres  of  dis- 
tilled w^ater  from  which  remove  portions  to  pressure  filter  as 
required. 

Decompose  0-5  gramme  of  the  substance  with  nitric-sulphuric 
acid;  add  60  to  100  c.c.  of  water  and  molybdate-nitrate  solution  in 
excess  until  solution  remains  clear  on  warming.  Filter  on  pressure 
filter  (about  five  minutes  required).  Add  more  molybdate-nitrate 
solution  till  all  yellow  precipitate  is  down.  Wash  the  precipitate 
with  water  till  free  from  acid  (but  not  too  long,  as  acid  may  separate 
out  of  the  precipitate).  Wash  precipitate,  pulp,  and  disc  (used  for 
supporting  paper  pulp  in  funnel)  into  a  beaker;  add  about  300  c.c.  of 
water  and  excess  .,  NaOH,  and  boil  for  ten  minutes  or  so  until 
NH3  passes  off.  Titrate  back  with  ^  H2SO4.  Boil  again  to  get  rid 
of  CO2,  and  finish  the  titration  with  a  drop  or  two  of  |  NaOH. 

One  molecule  P2O5  =56  molecules  NaOH. 

I  c.c.  I  NaOH  =1-268  milligrammes  PoOg. 

[200  c.c.  molybdate-nitrate  solution  =o-i  gramme  PoOj]. 


MEAT  233 


MEAT 


The  principal  food  animals  arc  cattle,  sheep,  pigs,  goats,  horses, 
the  buffalo  and  reindeer  in  a  few  countries,  and  in  Saxony  and  Italy 
dogs. 

Inspection  of  animals  before  slaughter  is  necessary  for  the  detec- 
tion of  infectious  diseases — anthrax,  glanders,  rabies,  etc. — and  for 
the  discovery  of  intoxications  in  which  meat  and  internal  organs  are 
but  slightly  altered. 

Of  the  many  pathological  conditions  which  affect  food  animals 
these  are  of  interest  in  laboratory  work:  Infective  granulations; 
a  few  diseases  produced  by  invisible  organisms ;  and  animal  parasites. 

Infective  granulations  are  found,  as  tuberculosis,  glanders,  and 
actinomycosis. 

To  determine  the  extent  of  tuberculosis  in  slaughtered  animals,  it  is 
necessary  to  make  a  methodical  inspection  of  the  hung-up  carcase 
from  above  downwards.  The  meat  is  first  examined,  and  after- 
wards the  lymphatic  glands,  which  receive  the  lymph  from  the 
meat,  in  the  following  order:  (i)  Popliteal,  inguinal  (superficial  and 
deep),  pubic,  or  supramammary  lymph-glands.  (2)  Iliac  and  retro- 
peritoneal lymph-glands.  (3)  The  lymph-glands  along  the  sides 
of  the  vertebral  column,  ribs,  and  sternum.  (4)  Prescapular  and 
axillary  glands.  (5)  Pharyngeal  and  submaxillary  lymph-glands. 
On  completion  of  the  examination  of  the  lymphatic  glands  of  the 
carcase,  the  internal  organs  with  their  lymphatic  glands  are  next 
examined — viz.,  the  kidneys  and  renal  lymphatics,  the  spleen,  liver, 
lungs,  and  the  udder  in  female  animals. 

Lastly  the  peritoneum  and  pleurse  are  systematically  inspected. 
Actinomycosis  occurs  as  small  or  large  tumours  delimited  from  the 
surrounding  tissues  by  a  thick  wall  of  dense  connective  tissue  in  the 
jaws,  tongue,  skin  of  head  and  neck,  and  much  more  rarely  in  the 
lungs,  liver,  kidneys,  udder,  and  abdominal  wall. 

Sections  and  smears  containing  Bacilhis  Uiberculosis  are  readily 
prepared  and  stained  with  Ziehl-Neelsen's  carbol-fuchsin,  and 
counterstained  with  methylene  blue. 

Glanders  must  be  distinguished  from  bovine  farcy,  not  trans- 
missible to  man,  and  produced  by  a  fungus  of  the  genus  Discomyces. 

The  ass  is  more  susceptible  to  glanders  than  any  other  animal. 


234  PRACTICAL  SAXITARY  SCIEXCE 

If  a  little  discharge  from  the  nose  be  rubbed  into  a  few  scarifications 
on  the  skin  of  the  forehead,  an  nedematous  swelling  rapidly  appears, 
followed  b}'  ulceration  along  the  lines  of  the  scratches;  the  tem- 
perature quickly  rises  to  40°  C.  or  41°  C.  The  neighbouring  glands 
swell,  a  discharge  from  the  nose  appears,  and  the  animal  dies 
in  a  few  days.  The  chocolate-coloured  growth  of  the  glanders 
bacillus  {B.  mallei)  on  potato  is  characteristic.  Microscopically 
B.  mallei  is  a  small  straight  rod  (3  to  5  /x),  with  rounded  ends.  It  is 
non-motile,  non-sporing,  and  Gram-negative. 

Sections  and  smears  containing  the  filaments  of  actinomyces  bovis 
stain  well  b}'  Gram's  method  and  by  carbol-fuchsin.  The  micro- 
scopic appearances  in  both  cases  are  unmistakable.  Some  difficulty 
may  be  experienced  in  isolating  the  parasite  from  pus  in  artificial 
culture,  as  the  pj'ogenic  organisms  overrun  the  media  before  the 
actinomyces  has  had  time  to  start.  Spread  pus  containing  the 
yellow  granules  on  a  couple  of  gelatin  plates,  and  incubate  at  22°  C. 
for  two  days.  Most  of  the  grains  will  be  surrounded  b}'  colonies  of 
contaminating  organisms,  but  a  few  will  be  found  here  and  there 
discrete  and  isolated;  pick  these  off  with  a  stout  platinum  wire,  and 
inoculate  three  or  four  coagulated  serum  slopes,  and  incubate  at 
37°  C.  In  live  or  six  days  (note  time  as  compared  with  a  possible 
CcLse  of  tubercle)  colonies  of  actinomyces  begin  to  grow.  Sown  in 
glycerin  broth,  hemispherical  colonies  appear  in  the  same  time  (five 
to  six  days),  as  large  as  a  small  pea,  and  fall  to  the  bottom,  leaving 
the  medium  clear. 

On  glycerin-agar  growth  occurs  in  two  days,  which  later  becomes 
yellowish- white,  dry,  and  wrinkled. 

On  potato  in  six  to  seven  days  small  colourless  colonies  appear, 
which  quickly  become  grey,  yellow,  and  tinall}'  wrinkled  and  edged 
with  black. 

The  invisible  organisms,  or  so-called  fiUrahle  viruses,  producing 
diseased  conditions  in  food  animals,  are  those  of  pleuro-pneumonia, 
foot-and-mouth  disease,  rinderpest,  horse-sickness,  swine-fever,  cow- 
pox,  sheep-pox,  and  bird-plague.  Prior  to  1898  laborator}^  methods 
failed  utterl}'  to  throw  an\-  light  on  the  causative  agents  operating 
in  these  diseases.  In  that  year  Nocard  and  Roux  devised  a  new 
method  of  investigation. 

In  pleuro-pneumonia  the  essential  lesion  is  the  distension  of  the 


ME  A  T  235 

meshes  of  the  interlobar  connective  tissue  witii  mucli  clear,  amber- 
coloured  fluid.  Subcutaneous  inoculation  of  this  fluid  in  another 
animal  reproduces  the  disease,  but  the  microscope  and  ordinary 
methods  of  cultivation  are  useless  in  searching  for  the  micro- 
organism. Nocard  and  Roux  filled  collodion  sacs  sown  with  a  drop 
of  the  fluid  from  a  case  of  pleuro-pneumonia,  and  introduced  them 
into  the  peritoneal  cavities  of  rabbits.  In  two  to  three  weeks  the 
contents  become  cloudy.  Microscopical  examination  with  a  mag- 
nification of  2,000  diameters  show  motile  retractile  points  so  small 
that  their  shape  cannot  be  determined;  these  cannot  be  stained. 
By  the  twentieth  day  the  virus  has  produced  in  the  rabbit  extreme 
emaciation,  but  no  lesion;  the  organs  and  body  fluids  arc  sterile. 
The  control  animals  in  which  similar  but  sterile  sacs  are  inserted 
remain  healthy.  It  would  appear  that  rabbits  are  immune  to  the 
organism,  but  susceptible  to  the  toxin.  The  contents  of  the  sacs 
cannot  be  cultivated  on  ordinary  media.  After  much  experimenta- 
tion these  observers  devised  a  medium  on  which  the  organism  can 
be  grown.  This  consists  of  i  part  of  rabbit's  serum  and  20  parts 
of  Martin's  peptone  solution  (mix  200  grammes  of  cleaned  and 
minced  pigs'  stomachs,  10  grammes  of  HCl,  i  litre  of  water  at  50°  C. ; 
heat  to  boiling  to  destroy  pepsin,  and  pass  through  cotton-wool; 
heat  the  filtrate  to  80°  C,  and  neutralize  at  this  temperature;  filter 
through  Chardin  paper,  and  autoclave  the  filtrate  for  four  or  five 
minutes  at  120°  C. ;  run  10  c.c.  of  the  clear  filtrate  into  test-tubes, 
and  sterilize  for  twenty  minutes  at  115°  C).  Tubes  of  this  medium 
sown  aerobically  with  a  drop  of  exudate  or  of  the  contents  of  the 
collodion  sacs,  and  incubated  at  37°  C,  produce  a  virulent  growth 
resembling  in  its  microscopical  and  other  characters  that  of  the 
sacs. 

This  disease  runs  both  an  acute  and  chronic  course.  In  the  acute 
form  the  respiratory  symptoms  are  most  marked. 

The  exudate  filtered  through  a  Chamberland  (F)  bougie  fails  to 
produce  the  disease  and  to  give  cultures. 

In  experiments  with  ultramicroscopic  viruses  it  is  necessary  to 
use  a  new  and  sterilized  filter,  and  not  to  allow  more  than  two  hours 
for  the  filtration  process,  nor  a  temperature  above  20°  C.  The 
pressure  of  filtration  should  be  as  low  as  possible,  and  the  emulsion 
should  be  diluted  to  prevent  blocking  of  the  pores  of  the  filter  with 


236  PRACTICAL  SANITARY  SCIENCE 

albuminous  matter.  Several  animals  shovild  be  inoculated  with  a 
large  volume  of  the  filtrate. 

Foot-and-mouth  disease  infects  cattle,  sheep,  goats,  and  pigs, 
and  is"  transmissible  to  man.  Aphthous  lymph  loses  its  infectivity 
when  kept  for  five  to  six  weeks.  Loffler,  liy  mixing  such  old  lymph 
with  fresh  lymph,  attenuated  by  heating  for  hve  minutes  at  60°  C, 
has  been  able  to  produce  immunity  in  oxen. 

Bird-plague  virus  has  been  grown  by  Marchoux  on  defibrinated 
fowl  blood  spread  on  glucose-peptone-agar,  and  incubated  at  37°  C. 
Growth  occurs  in  the  zone  of  blood  adjoining  the  surface  of  the  agar. 

Animal  Parasites  in  Meat. — Three  groups  of  animal  parasites 
may  be  recognized :  I.  Parasites  not  transmissible  to  man.  II.  Para- 
sites which  may  be  transmitted  to  man  by  eating  meat.  III.  Para- 
sites not  immediately  harmful,  but  which  may  become  so  after  a 
preliminar}.'  change  of  host. 

1.  Parasites  not  transmissible  to  Man  —  i.  The  Hair- 
Follicle  Mite  in  the  Skin  of  Hogs  {Demodex  phylloides  suis). — It  is 
from  0-2  to  0-25  milhmetre  long,  and  produces  small  swellings  of 
the  hair-follicles,  greyish-yellow  in  colour,  and  containing  disinte- 
grated epithelial  cells  and  dermal  oil. 

2.  Dipterous  LarvcB. — Larva  of  warble  fly  {CEsirus  bovis),  28  x  15 
millimetres,  found  in  subcutis,  causes  considerable  loss  to  cattle- 
raisers  through  deterioration  of  flesh  and  skins.  It  is  found  in  the 
fjesophagus  from  July  to  September,  in  the  spinal  canal  from  Sep- 
tember to  January,  in  the  subcutis  and  skin  from  January  to  -May. 
Other  larvae  are  the  Gastrophilns  equi  and  G.  nasalis. 

3.  Numerous  Worms  which  appear  in  Organs  of  Food  Animals. — 
(a)  All  tapeworms  except  Tccnia  echinococcus  of  the  dog,  such  as 
Moniezia  expansa  found  in  lambs,  Drepanido  tcenia  lanceolata  and 
D.  setigera  in  geese,  Davainea  tetragona  in  young  fowls,  Taenia 
coemirus,  T.  marginata,  and  T.  serrata,  in  the  dog.  (b)  Larval  stages 
of  all  tapeworms,  except  Cysticercus  bovis,  C.  celluloses,  and  Echino- 
coccus polymorphus,  such  as  Tcenia  ccenurus  {Coenurus  cerebralis), 
which  causes  the  disease  known  as  '  gid  '  in  sheep,  and  Cysticercus 
tenuicollis  (larva  of  T.  marginata)  found  in  sheep,  pigs,  and  cattle. 
(f)  Flukes  (Trematodes),  such  as  Distoma  hepaticum  and  D.  lanceola- 
tnm,  found  in  the  liver  of  the  sheep.  These  flat  organisms  measure 
as  much  as  25  x  13  millimetres.     They  are  covered  with  scale-like 


MEAT  237 

spines  on  the  integument,  which  irritate  the  bile-ducts  where  they  arc, 
located,  and  cause  the  thickening  of  these  vessels  so  characteristic  of 
the  condition.  They  may  wander  from  the  liver  to  the  lungs.  Their 
embryonic  stages  are  passed  in  a  free  condition  in  molluscs,  mostly 
water-snails.  Apart  from  the  catarrh  and  cirrhotic  condition  of 
bile-ducts  produced  by  these  parasites,  hsemorrhages  occur,  and 
the  health  of  the  affected  animals  may  be  seriously  damaged. 
(d)  Round-worms  (Nematodes),  with  single  exception  of  Trichina 
spiralis,  such  as  Ascarus,  Eustrongylus,  Filaria  (Schneider's  group 
Polymyaria),  Oxyuris,  Strongylus  (Schneider's  Meromyaria),  Tri- 
china spiralis,  Trichocephalus,  Anguillula  (Schneider's  Holomyaria). 
II.  Parasites  which  may  be  transmitted  to  Man  by  eating- 
Meat. — I.  The  Beef  bladder  worm  {Cysticercus  bovis),  which  is  the 
larval  form  of  Tcenia  saginata  of  man,  known  also  as  T.  medio- 
canellata,  consists  of  a  somewhat  elongated,  roundish  bladder  located 
in  the  interfibrillar  connective  tissue  of  the  striated  musculature, 
and  occasionally  in  lungs,  liver,  and  brain.  The  grey  transparent 
bladder  consists  of  a  connective-tissue  capsule  produced  by  reaction 
in  surrounding  tissues,  and  of  the  parasite.  The  latter  consists  of  a 
scolex  and  caudal  bladder  filled  with  fluid ;  the  scolex  possesses  four 
suckers,  but  no  hooks.  The  size  of  the  cysticercus  varies  from  that 
of  a  pinhead  to  tliat  of  a  small  pea. 

2.  The  Pork  bladder  worm  {Cysticercus  celhdoscs)  is  the  larval 
stage  of  TcBuia  solium.  In  macroscopic  appearances  and  location 
between  muscle  fibres  it  closely  resembles  C.  bovis.  For  the  rest,  the 
cyst  is  more  transparent,  so  that  the  scolex  when  invaginated  into 
the  caudal  bladder  appears  more  clearly.  The  scolex  has  twenty- 
two  to  twenty-eight  hooks  in  a  double  circle;  the  hooks  are  of 
compressed  shape,  stout  at  the  base  and  with  slightly  curved  points. 
The  cysticerci  prefer  the  lumbar  and  abdominal  muscles,  pillars  of 
the  diaphragm,  intercostal  and  masticatory  muscles. 

3.  Trichina  Spiralis. — Hilton  investigated  calcified  trichinse  in 
1832.  Zenker  discovered  trichinosis  in  Dresden  in  i860.  After 
ingestion  of  trichinous  meat,  sexually  mature  trichinse  develop  in 
the  intestines  of  certain  mammals;  the  parasite  is  set  free  from  its 
capsule  b}^  the  gastric  juice.  Males  and  females  copulate,  and  the 
females  deposit  enormous  numbers  of  embryos.  Leuchart  assumed 
that  the  embryos  bore  their  way  out  of  the  intestine  into  the  peri- 


23S  PRACTICAL  SAXITARY  SCIEXCE 

toneal  and  thoracic  cavities,  and  ultimately  reach  the  muscles. 
Heitzmann  argues  that  this  migration  cannot  possibly  take  place  in 
the  few  days  that  elapse  lx;t\veen  the  swallowing  of  infected  meat 
and  the  appearance  of  embryos  in  the  muscles,  and  that  the  embryos 
are  conveyed  by  the  blood-stream,  and  caught  as  emboli  in  the 
capillaries.  Arrived  in  the  muscles,  a  capsule  is  formed  which  in  due 
course  becomes  calcified.  The  frequent  occurrence  of  the  parasite 
in  rats  is  explained  by  the  presence  of  the  rat  in  abattoirs,  knackers' 
yards,  etc.  Degeneration  of  trichinae  in  their  capsules  frequently 
takes  place.  The  muscles  most  likely  to  contain  parasites  are  those 
of  the  tongue  and  larynx,  and  the  pillars  of  the  diaphragm. 

Rhabditides  (larvpe  of  strongylidce)  may  be  mistaken  for 
trichinae. 

III.  Parasites  not  immediately  Harmful  to  Man,  but  which 
may  become  so  after  a  Preliminary  Change  of  Host  — 
I.  EcJiinococci.- — {n)  Tccnia  echinococcns  resides  as  a  parasite  in  the 
small  intestine  of  the  dog,  and  is  the  asexual  stage  of  a  tapeworm 
with  three  to  four  segments.  It  is  2  to  6  millimetres  long  by  0-3  to 
0-5  millimetre  wide.  It  possesses  a  protruding  rostellum  with 
twenty-eight  to  fifty  hooks.  The  last  proglottid  is  2  millimetres 
long,  and  contains  mature  eggs. 

The  echinococci  occur  in  two  chief  forms — (a)  E.  unilociilaris  and 
(6)  E.  muUilocnlaris.  E.  nnilocularis  forms  simple  cysts  surrounded 
by  connective  tissue;  in  some  cases  daughter  cj'sts  are  developed 
from  the  mother  cysts,  in  other  cases  not. 

E.  multilocularis  forms  daughter  cysts  by  constriction  from  a 
central  mother  cyst,  which  in  turn  are  furnished  with  the  same 
reproductive  power.  The  daughter  cysts  do  not  remain  in  the 
mother  cyst  or  inside  the  organic  membrane  formed  about  it,  but 
after  constriction  become  separated  from  the  mother  cyst  by  con- 
nective tissue.  Accordingly,  the  vesicles  attain  no  great  size,  but 
lie  in  the  connective  tissue  like  the  epithelia  of  an  acinous  gland. 
The  hooks  of  the  multilocular  form  are  somewhat  larger  than  those 
of  the  unilocular. 

The  intermediate  host  is  man. 

The  E.  unilociilaris  occurs  in  the  liver,  lungs,  and  spleen,  of  the 
ox,  sheep,  and  pig,  and  less  often  in  the  heart,  kidneys,  lymph- 
glands,  muscles,  and  marrow  cavities  of  bones. 


MEAT  239 

The  E.  muUilocidans  occurs  in  the  liver  of  bovincs,  forming 
tumours  of  various  sizes  which  exhibit  a  constant  growth. 

2.  Larvce  of  Pentastomum  Tcenioides. — These  are  flat  white  struc- 
tures, 4  to  5  milhmetres  long  by  i  to  1-5  millimetres  broad,  divided 
into  about  eighty  segments  furnished  with  backwardly-directed 
tooth-like  spines.  Below  the  mouth  there  are  two  slit-like  apertures 
on  either  side,  from  each  of  which  the  points  of  two  claws  protrude. 
These  openings  gave  origin  erroneously  to  the  name  Pentastomum 
(five-mouthed).  The  embryos  are  provided  with  a  boring  apparatus 
under  the  mouth  opening,  and  at  the  opposite  end  of  the  body  are 
several  spines  which  serve  for  locomotion. 

Tlie  parasites  are  found  in  hares,  goats,  sheep,  and  more  rarely  in 
cattle,  under  the  peritoneum,  in  the  liver,  in  the  mesenteric  glands, 
and  in  the  lungs. 

Dogs  are  the  chief  source  of  pentastome  larvae,  and  man,  through 
intimate  association  with  the  dog,  may  become  infected  by  ingestion 
of  pentastome  eggs. 

A  subdivision  of  the  Protozoa — viz.,  the  Sporozoa — are  of  some 
importance  in  meat  inspection.  This  subdivision  consists  of  the 
following  orders:  Coccidia,  Myxosporidia,  Sarcosporidia,  and 
Hsematosporidia. 

The  Coccidia  are  parasites  of  epithelia,  and  occur  in  the  liver  of 
the  rabbit  and  other  animals,  and  occasionally  in  the  liver  of  man. 
C.  perforans  occurs  in  the  intestinal  epithehum  of  rabbits,  sheep, 
and  calves,  and  causes  a  catarrhal  diarrhoea. 
Myxosporidia  are  chiefly  parasitic  in  fish. 

Sarcosporidia  (Miescher's  sacs)  occur  in  hogs,  mostly  in  the 
striated  muscles. 

HcBmatos-poridia. — Theobald  Smith's  discovery  of  the  organism  of 
Texas  fever  in  cattle  conferred  an  importance  on  this  group  in 
relation  to  meat  inspection,  which  with  the  constant  discovery  of 
new  forms  ever  increases. 

The  flesh  of  different  animals  differs  materially  in  appearance. 
Veal,  mutton,  and  pork,  are  lighter  in  colour  than  beef.  The 
method  of  slaughter  has  something  to  do  with  this,  as  in  those  cases 
where  free  bleeding  takes  place  the  flesh  is  of  a  lighter  hue  through 
loss  of  hemoglobin.  The  flesh  of  young  animals,  containing  as  it 
does  less  haemoglobin,  is  also  lighter  in  tint. 


240 


PRACTICAL  SANITARY  SCIENCE 


Fig.  6o. —  Head  of  Cysticercus.     x  20. 


Fig.  61. — TAENIA  Solium       x  4. 


There  is  a  widespread  feeling  in  this  country,  not  by  any  means 
founded  upon  knowledge,  that  the  carcase  of  an  animal  which  has 


ME  A  T 


241 


Fig.  62. — Trichina  Spiralis,     x  100. 


Fig.  63. — Head  of  Distoma  Hepaticum.     x  4. 

died  of  any  disease  should  not  be  used  as  food.  In  certain  cases 
this  is  obviously  correct,  but  in  others  there  is  no  evidence  to  show 
that  the  edible  parts  are  in  any  way  deteriorated  as  food  materials. 

16 


242  PRACTICAL  .s\-i.V7  7.-i/eV  SCIEXCE 

Flesh  containing  infective  parasites,  and  flesh  which  is  in  a 
state  of  putrefaction,  inchiding  '  high  '  game,  should  be  rigorously 
excluded  from  human  consumption. 

Good  fresh  meat  possesses  certain  well-recognised  characters  which 
are  easy  of  detection.  It  is  Arm  and  somewhat  elastic  to  the  touch, 
pointing  to  the  fact  that  rigor  mortis  is  well  developed.  It  is  dry 
on  section,  of  a  clear  red  colour  and  acid  reaction.  A  section  through 
the  whole  thickness  of  a  joint  presents  a  uniform  appearance.  The 
odour  of  fresh  meat  may  be  obtained  by  running  a  clean  wooden 


Fig,  64. — AscARUs  Lumbricoides.     x  7. 

skew'er  down  to  the  bone,  and  withdrawing  and  smelling  it.  The 
fat  is  firm,  and  not  too  yellow  in  colour.  Old  animals  and  those  fed 
on  oil-cakes  exhibit  fat  of  a  deep  yellow  colour.  The  bone-marrow 
is  bright  red,  and  coagulates  within  twenty-four  hours. 

The  lymphatic  glands  arc  of  normal  size,  colour,  and  consistence. 

The  ash  contains  a  normal  quantity  of  phosphoric  acid  and  salts 
of  potash. 

When  cooked,  meat  should  not  lose  more  than  30  per  cent,  of 
its  weight,  and  when  dried  on  a  water-bath  to  constant  weight  it 
should  not  lose  more  than  75  per  cent. 


MEA  T  243 

Bad  meat  may  present  many  evil  characters.  A  deep  purple 
colour  points  to  acute  septicemia,  pulmonary  disease  ending  in 
asphyxia,  or  when  found  in  patches  to  hypostatic  congestion.  The 
odour  may  be  that  of  advanced  putrefaction,  or  it  may  be  urinous, 
as  in  uraemia.  There  is  absence  of  elasticity  in  a  section  when 
pitted  with  the  finger;  some  parts  are  softer  than  others,  and  the 
flesh  may  be  generally  sodden  and  dropsical.  The  fat  is  highly 
coloured,  soft,  and  perhaps  hgemorrhagic.  The  juice  expressed 
from  unsound  meat  is  alkaline  in  reaction  from  the  formation  of 


Fig.  65. — OxYURis  Vermicularis.     x  20. 

ammonias.  At  later  stages  the  meat  becomes  green,  and  even 
black,  when  no  critical  examination  is  required  to  establish  its  con- 
dition. Certain  chemical  tests  have  been  devised  to  detect  putre- 
faction in  the  early  stages,  but  none  of  them  can  convey  more 
reliable  information  than  that  obtained  by  well-trained  eyes  and 
noses. 

The  carcases  of  animals  that  have  died  of  anthrax  and  allied 
conditions,  pyaemia,  and  septicaemia,  present  congested,  ecchy- 
mosed,  and  haemorrhagic  tissues.  In  all  cases  where  one  or  other 
of  these  diseases  is  suspected  the  offal  should  be  seen  and  carefully 
examined. 


244  PRACTICAL   SAXITARY  SCIEXCE 

Preservatives  in  Meat — Boric  Acid. — A  portion  of  finely- 
divided  nuat  mcchanioalh-  freed  from  fat  is  warmed  with  water 
acidulated  with  HCl.  The  extract  is  tested  with  turmeric.  Quanti- 
tative estimation  is  made  from  the  same  extract  as  under  milk. 

Salicylic  Acid. — A  portion  of  meat  freed  from  fat  as  above  is 
slightly  acidified  and  shaken  up  with  ether;  the  ether  extract  is 
evaporated  to  dryness,  and  the  residue  tested  in  aqueous  solution 
with  ferric  chloride.     A  violet  colour  indicates  sahcylic  acid. 

Formaldehyde. — This  preservative  may  be  used  as  a  solution,  and 
as  a  gas  in  meat-safes  and  the  holds  of  vessels  carrying  chilled  meats. 
Inside  safes  is  placed  a  receptacle  carrying  pastilles  of  polymerized 
formaldeh3'de — paraformaldehyde  or  trioxymethylene — which  is 
heated  until  the  paraformaldehyde  is  depolymerized  and  simple 
aldehyde  vapour  is  given  off.  The  meat  is  left  in  contact  with 
the  vapour  for  twenty  minutes  or  more.  In  the  holds  of  vessels 
formalin  is  evaporated  in  the  presence  of  the  quarters  of  dressed 
meat  in  the  proportion  of  lo  ounces  to  i,ooo  cubic  feet  of  space. 
Fomialdehyde  penetrates  the  substance  of  the  meat,  especially  areas 
not  covered  bj-  fat,  to  distances  extending  from  5  to  20  millimetres. 
The  proteins  and  amino-acids  of  meat  unite  with  formaldehyde 
to  form  methylene-imino  compounds,  as  demonstrated  by  Schiff. 
The  reaction  is  reversible,  and  only  proceeds  to  completion  in  the 
presence  of  excess  of  formaldehyde: 

CHa'NHa-COOH  +  H-CHO  -CH, :  X-CHo-COOH  +  H.,0. 

Amino-acetic  acid. 

Amino-acids  composed  of  basic  and  acid  groups  have  an  ampho- 
teric reaction;  when  treated  with  H'CHO  they  become  acid,  and 
the  amount  of  liberated  acid  can  be  readily  determined  by  titration 
with  standard  alkali:  hence  the  amount  of  formaldehyde  which 
enters  into  the  reaction  can  be  detemiined. 

The  colour  reactions  b}'  which  formaldehyde  can  be  detected  in 
milk  are  not  applicable  to  meat,  inasmuch  as  meat  gives  a  violet 
colour  when  heated  with  HCl  in  the  absence  of  formaldehyde 
(formation  of  hsematoporphyrin  from  Hb). 

Schryver  uses  the  following  test:  To  10  c.c.  of  the  water  in  which 
a  portion  of  meat  has  been  heated  for  five  minutes  in  a  boiling  water- 
bath,  add  2  c.c.  of  a  I  per  cent,  phenylhydrazine  hydrochloride 


MEAT  245 

solution.  Cool  and  filter  through  c(jtton-wool.  Add  i  c.c.  of  5  per 
cent,  potassium  ferricyanide  solution  and  4  c.c.  of  concentrated  HCl. 
A  brilliant  fuchsin-like  colour  is  formed,  which  in  a  few  minutes 
reaches  its  maximum  and  lasts  for  several  hours.  (The  ferricyanide 
oxidizes  the  aldehyde  condensation  product  to  a  body  which  is  a 
weak  base,  which  forms  a  scarlet  hydrochloride.  On  dilution  with 
water  this  body  hydrolyses,  forming  a  base  which  can  be  extracted 
with  ether  to  form  a  yellow  solution.  If  to  this  last  concentrated 
HCl  be  added,  the  base  passes  back  into  aqueous  solution  in  the 
form  of  the  scarlet  hydrochloride.) 

In  those  cases  in  which  the  formaldehyde  amounts  to  about 
I  in  50,000  parts  of  meat,  10  grammes  of  minced  meat  are  used  with 
10  c.c.  of  water.  Where  the  concentration  reaches  i  part  in  5,000 
meat,  10  grammes  of  meat  are  heated  with  100  c.c.  of  water  and 
20  c.c.  of  the  phenylhydrazine  hydrochloride  solution.  After  filter- 
ing and  cooling,  12  c.c.  of  the  filtrate  (as  above)  are  mixed  with  i  c.c. 
of  the  ferricyanide  and  4  c.c.  HCl. 

By  comparing  the  colour  obtained  with  carefully  prepared 
standards,  the  amount  of  formaldehyde  in  any  sample  of  meat  can 
be  determined  {see  Appendix). 

Bacterial  Food-Poisoningr  [cf.  L.G.B.  Food  Reports,  No.  18).— 
Three  groups  of  bacteria  appear  to  take  part  in  outbreaks  of  food- 
poisoning — viz.,  the  Gartner  group  of  hQ.c\\\\;  Bacillus  coli,  B.  proieus, 
etc. ;  and  B.  hotulinus. 

The  Gartner  group  {B.  enteritidis,  B.  snipestifer,  B.  paratyphosus  B, 
etc.)  has  been  found  responsible  for  many  outbreaks  of  poisoning 
through  eating  pork,  pork  pies,  pork  sausages,  brawm,  meat  and 
minced  and  baked  meat,  tinned  tongue,  tinned  salmon,  veal  pies, 
milk,  etc. 

The  B.  coli  group  has  been  found  in  milk,  meat  pies,  tinned  meat, 
etc.  B.  proteus  and  other  putrefactive  bacteria  are  occasionally 
found  in  cases  of  poisoning  by  sausages,  chilled  meat,  etc. 

B.  hotulinus  (studied  by  Van  Ermengem)  is  occasionally  respon- 
sible for  cases  of  sausage-poisoning. 

An  experimental  investigation  in  the  human  subject  on  the 
influence  of  boric  acid  and  borax  on  food,  by  Dr.  Harvey  W.  Wiley, 
United  States  Department  of  Agriculture,  was  published  in  1904, 
as  Bulletin  No.  84,  part  i.  Bureau  of  Chemistry,  Washington;  and 


246  PRACTICAL  SANITARY  SCIENCE 

a  further  similar  investigation  on  the  influence  of  saHcylic  acid  and 
saUcylates  was  published  in  1906,  as  part  2  of  the  same  bulletin. 
Wiley's  findings  on  the  influence  of  boric  acid  and  borax  were 
critically  reviewed  by  Professor  Oscar  Liebreich ;  an  English  trans- 
lation of  Liebreich 's  report,  dated  iqoO,  is  published  by  J.  and  A 
Churchill. 


ALCOHOLIC  BEVERAGES 

The  alcohols  (C„H2„+20)  may  be  regarded  as  oxygen  derivatives 
of  the  paraffins.  They  are  colourless  and  neutral  substances  pos- 
sessing neither  alkaline  nor  acid  reaction.  Those  with  few  carbon 
atoms  are  liquid;  the  higher  members  of  the  series  are  solid. 
Methyl,  ethyl,  and  propyl  alcohols  are  miscible  with  water;  butyl 
alcohol  dissolves  in  12  parts,  amyl  alcohol  from  fusel-oil  requires 
39  parts  of  water.  The  relative  proportion  of  oxygen  determines 
the  solubility  in  water;  as  ox3'gen  decreases  with  increasing 
molecular  weight,  the  physical  characters  of  the  paraffin  corre- 
spondingly predominate.  Alcohols  resemble  water  in  certain 
reactions,  in  others  caustic  alkalies.  They,  like  water,  liberate 
one  atom  of  H  when  treated  with  sodium,  and  retain  as  a  substitute 
one  atom  of  the  latter.  The  action  of  P,  Br,  etc.,  on  alcohols 
results  in  compounds  similar  in  structure  to  those  formed  from 

water : 

2H.,0  +  Na,  =  2H0Na  +  H.. 
2CH40(methyl  alcohol)  +  Na,"=  2CH50Na  +  H,. 
H„0  +  PCir-  2HCI  +  POCI3." 
CH4O  +  PCI5  =  CH,C1  +  HCl  +  POCI3. 
3H.,0  +  PBr3  =  sHJBr  +  H3PO3. 
3CH4O  +  PBr^  =  sCHgBr  +  H3PO3. 

The  similaritv  in  constitution  between  alcohols  and  caustic  alka- 
lies is  seen  by  the  following  reactions : 

NaOH  +  HCl  =  NaCl  +  H.,0. 
CH4O  +  HCl  -  CH3CI  +  H.,0. 
NaOH  +  HoSOj  =  NaH  SO^  +  H.,0. 
CH4O  +  Ha^SO^  -  CH3HSO4  +  H.O. 

It  follows,  then,  that  the  graphic  formula  of  an  alcohol  may  be 
constructed  in  the  same  manner  as  that  for  water  and  caustic  soda: 


ALCOHOLIC  Li  EVER  AGES  247 

H 

H— 0-H  Na— 0— H  H— C— 0— H. 

I 
H 

The  different  alcohols  do  not  behave  alike  on  oxidation.  Some 
form  aldehydes,  others  ketones.  This  difference  in  behaviour  on 
oxidation  divides  them  into  three  groups — primary,  secondary,  and 
tertiary  alcohols.  A  primary  alcohol  has  the  hydroxyl  group 
linked  to  an  end  carbon  atom  of  a  straight  chain,  and  contains  the 
group  -CHalOH).  A  secondary  alcohol  has  the  hydroxyl  group 
attached  to  a  middle  carbon  atom  of  a  straight  chain,  and 
contains  the  group  .•CH{OH).  In  a  tertiary  alcohol  the  carbon 
atom  attached  to  the  hydroxyl  group  is  linked  to  three  carbon 
atoms  :C(OH). 

Methyl  alcohol,  CH3(0H),  has  a  specific  gravity  0-812,  and 

boiling-point  66°  C. 
Ethyl  alcohol,  C2H5(OH),  has  a  specific  gravity  o-8o6,  and 

boiling-point"78°  C. 
Propyl  alcohols,  C3H7(OH). 
Propyl   alcohol   (primary),  CH3CHoCH2(OH),   has   a   specific 

gravity  0-804,  ^^'^  boiling-point  97°  C. 
Propyl  alcohol  (secondary),  CH.,-CH(0H)-CH3,  has  a  specific 

gravity  0-789,  and  boiling-point  81°  C. 
Butyl  alcohols,  C4H9(OH). 
Butyl   alcohol    (normal    primary),  C^-^-CH.j^-CR^-OK,  has    a 

specific  gravity  0-810,  and  boiling-point  117°  C. 
Butyl  alcohol  (normal  secondary)  C2H5-CH(OH)-CH3,  has  a 

boiling-point  100°  C. 
Butyl  alcohol  (tertiary),  (CH3)2C(OH)-CH3,  hasaspecificgravity 

0-786,  and  boiling-point  83°  C. 
Amyl  alcohols,  C5Hu(0H). 
Normal  primary,  CoH5-CHo-CH2-CH2(OH),  has  a  specific  gravity 

0-815,  3-nd  boiling-point  138°  C. 
Isobutyl  carbinol,   (CH3)2-CH-CHo-CH,(OH),  has    a    specific 

gravity  0-810,  and  boihng-point  131°  C. 
Secondary   butyl   carbinol,   CH3-CH-(C.,H5)-CH2(OH),    has    a 

boihng-point  128°  C. 
Methyl  propyl  carbinol,  CoHj-CH^-CHOH-CHg,  has  a  boiling- 
point  119°  C. 
Diethyl  carbinol,  C.2H5-CHOH-C2H5,  has  a  boihng-point  117°  C. 


248  PRACTICAL  SANITARY  SCIEXCE 

The  primary  alcohols  on  oxidation  lose  two  atoms  of  hydrogen 
and  form  aldehydes;  the  latter,  on  continued  oxidation,  take  up 
one  atom  of  oxygen,  and  are  converted  into  acids. 

Ethj'l  alcohol  ^aelds  acetaldehyde,  and  then  acetic  acid: 


CH3  I  CH; 


3 

I  I 

H— C— 0-,-H  +  0=H— C=0  +  H,0. 

I 

H 
CH3  CH3 

H— C=0  +  0     =H0— C  =  0. 

The  secondar\^  alcoliols  yield  up  two  atoms  of  hydrogen  in  the 
first  stage  to  form  ketones.  Further  oxidation  forms  acids  con- 
taining fewer  carbon  atoms  than  the  ketones. 

The  tertiary  alcohols  decompose  on  oxidation,  fonuing  ketones, 
or  acids  containing  fewer  carbon  atoms  than  the  alcohol.  The 
alcohols  are  found  as  constituents  of  man\.'  natural  products,  such 
as  fats,  oils,  waxes,  etc.  They  are  prepared  mainly  by  fermenta- 
tion. Eth\i,  propyl,  butyl,  and  amyl  alcohols  arc  all  produced  in 
this  way.  Methyl  alcohol  is  obtained  by  the  distillation  of  wood,, 
and  by  the  destructive  distillation  of  the  by-products  of  the  beet- 
sugar  industry.     Commercial  methyl  alcohol  contains  acetone. 

When  yeast  is  added  to  a  solution  of  grape-sugar  or  cane-sugar, 
the  liquid  froths  and  appears  to  boil ;  the  sugar  is  broken  up  into 
ethyl  alcohol  and  carbon  dioxide.  Pasteur  described  this  as  the 
result  of  life  without  oxygen,  the  yeast  cells  being  able  in  the 
absence  of  free  oxygen  to  use  combined  oxygen  liberated  in  the 
decomposition  of  the  sugar  or  other  substance.  Many  explanations 
of  the  phenomenon  were  offered  by  observers  in  a  controversy 
which  has  lasted  for  many  years. 

In  1896  Buchner  discovered  accidentally  that  yeast-juice  (free 
from  cells),  to  which  sugar  had  been  added  in  order  to  prevent 
putrefaction,  fermented  the  sugar;  on  heating  the  juice  to  50°  C. 
its  power  of  fermentation  was  destroyed.  He  concluded  that  the 
production  of  alcoholic  fermentation  does  not  require  so  compli- 
cated an  apparatus  as  the  yeast  cell,  and  that  femicntation  was 
effected  by  a  dissolved  substance  in  the  cell  to  which  he  gave  the 


ALCOHOLIC  BEVERAGES  249 

name  of  "  zymase."  Yeast-juice  contains  a  powerful  tryptic 
enzyme.  Zymase  when  it  has  acted  for  some  time  disappears, 
and  Buchner  conchided  that  it  was  destroyed  by  the  endotrypsin. 
When  a  mixture  of  alcohol  and  ether  is  added  to  juice,  a  precipitate 
is  formed  which  can  be  dried  to  an  amorphous  powder  (zymin)  of 
high  fermentative  activity. 

The  action  of  living  yeast  appears  to  follow  the  same  law  as  that 
of  most  enzymes — viz.,  the  enzyme  unites  with  the  fermentable 
material  (substrate  or  zymolyte),  forming  a  compound  which  only 
slowly  decomposes,  so  that  it  remains  in  existence  for  a  perceptible 
interval  of  time.  The  rate  of  fermentation  depends  on  the  rate  of 
decomposition  of  this  compound,  and  hence  varies  with  its  con- 
centration. 

It  has  been  shown  by  Harden  that  the  addition  of  a  soluble 
phosphate  to  a  fermenting  mixture  of  a  hexose  with  yeast- juice  or 
zymin  causes  the  production  of  an  equivalent  quantity  of  carbon 
dioxide  and  alcohol,  which  fact,  it  is  concluded,  indicates  that  a 
definite  chemical  reaction  occurs  in  which  sugar  and  phosphate 
are  concerned.  An  equation  can  be  constructed  embodying  two 
molecules  of  sugar  in  action  in  which  carbon  dioxide  and  alcohol 
are  equal  in  weight  to  half  the  sugar  used,  and  hexosephosphate 
and  water  to  the  other  half : 

2CfiHi20e  +  2PO4HR2  =  2CO2  +  2C2H6O  +  2H2O  +  CeHioOiCPO^Ra).^. 

The  main  difference  between  fermentation  by  yeast-juice  and  by 
the  living  cell  appears  to  consist  in  the  rate  of  decomposition  of  the 
hexosephosphate.  A  comparison  of  living  yeast,  Z5^min,  and  yeast- 
juice,  shows  that  these  form  an  ascending  series  with  respect  to 
their  response  to  phosphate.  Using  fructose  as  the  zymolyte, 
yeast  does  not  respond  to  phosphate  at  all,  the  rate  of  fermentation 
by  zymin  is  doubled,  and  that  by  yeast- juice  increased  twentv  to 
forty  times.  It  may  be  that  the  balance  of  enzymes  in  the  living 
cell  is  such  that  the  supply  of  phosphate  is  maintained  at  the 
optimum,  and  a  further  supply,  consequently,  does  not  alter  the 
rate  of  fermentation. 

Although  alcohol  is  the  principal  constituent  by  which  such 
beverages  affect  the  nutrition  of  the  body,  it  must  not  be  forgotten 
that  in  many  cases  ethers,  aldehydes,  and  other  bj'-products  of 


250  PRACTICAL  SAXITARY  SCIEXCE 

fermentation,  are  likewise  found.  Alcohol  to  the  extent  of  i  per 
cent,  seems  to  be  favourable  to  a  digesting  mixture  in  the  stomach ; 
10  per  cent,  slightly  retards  gastric  digestion,  and  20  per  cent, 
arrests  it.  Pancreatic  digestion  is  much  more  sensitive  to  alcohol ; 
but  as  digestion  is  not  only  a  chemical  process,  but  greatly  in- 
fluenced by  the  movements  of  the  stomach  and  other  factors  differ- 
ing widely  in  different  individuals,  it  is  not  surprising  to  find  that 
alcohol  has  ver\'  different  effects  in  its  relation  to  individual  cases. 
It  is  admitted  on  all  hands  that  it  quickens  the  activity  of  stomach 
movements  and  secretions.  If  the  retarding  influence  of  alcohol 
on  the  chemical  part  of  digestion  be  weighed  against  its  quickening 
influence  on  the  flow  of  gastric  juice  and  on  gastric  peristalsis,  the 
balance  is  in  favour  of  its  use  as  a  digestive  stimulant.  In  certain 
conditions  of  disease  these  properties  are  greatly  enhanced.  Alcohol, 
unlike  water,  is  freely  absorbed  b}'  the  mucous  membrane  of  the 
stomach,  and  requires  no  digestion.  It  passes  into  the  blood  at 
once.  Not  only  is  it  rapidly  absorbed  itself,  but  it  assists  the 
absorption  of  other  bodies.  Whilst  it  passes  from  the  stomach 
into  the  blood,  water  passes  from  the  blood  into  the  stomach: 
the  endosmotic  equivalent  of  alcohol  is  4-2,  which  means  that,  for 
every  gramme  of  alcohol  passing  through  an  animal  membrane  in 
one  direction,  4-2  grammes  of  water  pass  in  the  opposite. 

Alcoholic  beverages  are  all  in  a  broad  sense  saccharine  products, 
the  result  of  the  fermentation  of  sugar.  In  fruits  sugar  exists  in 
the  juice,  which  on  exposure  to  the  air  ferments: 

C6Hi.A=2CO.,  +  2C,,HeO. 

In  grain  a  preliminary'  fermentation  takes  place — starch  is  con- 
verted into  sugar: 

2CeH,oO,,  +  H,0  =  CeH.o  O^  +  CeH,  A- 

(starch)  (dextrin)  (dextrose) 

C,Hio05  +  H.30  =  CeHiA 

(dextrin)  (dextrose) 

Beer. 

In  making  beer,  barley  is  steeped  in  water  and  spread  in  layers  a 
few  inches  deep  on  floors,  where  a  temperature  favourable  to  germi- 
nation is  maintained.  Diastase  is  formed  in  the  grain.  When 
germination  has  proceeded  sufficiently,  the  grain  is  dried  on  a  kiln, 


ALCOHOLIC  BEVERAGES  251 

and  is  known  as  malt.  The  malt  is  mixed  witli  water  at  fxP  to 
65°  C,  and  the  diastase  rapidly  converts  the  starch  into  dextrin  and 
maltose.  The  extract,  or  wort,  is  run  into  copper  pans  and  boiled, 
with  addition  of  hops.  The  liquid  is  now  rapidly  cooled  to  15''  to 
17°  C.  and  drawn  into  vats ;  yeast  is  added,  and  the  maltose  alone 
undergoes  fermentation.  As  this  sugar  forms  only  a  small  portion 
of  the  extract,  the  quantity  of  alcohol  is  not  large.  The  addition 
of  glucose  to  the  boiling-pan  increases  the  amount  of  alcohol. 

The  wort  is  capable  of  growing  other  bacteria  than  yeast,  and 
if  great  care  is  not  taken  secondary  fermentations  occur,  and  pro- 
duce diseased  beers. 

In  brewing,  the  temperature  largely  affects  the  character  of 
fermentation.  Slow  fermentation,  known  as  '  bottom  fermenta- 
tion,' in  which  the  yeast  settles  out  at  the  bottom,  proceeds  at 
6°  to  8°  C.  Top  fermentation,  in  which  the  yeast  is  carried  to  the 
surface,  occurs  at  16°  to  18°  C,  and  is  not  so  easily  controlled. 
The  yeast  cells  in  either  case  feed  on  the  dextrin,  maltose,  peptones, 
and  amides  of  the  wort. 

Lager  beers  contain  a  low  proportion  of  hops  (female  flower  of 
Humulus  lupuhis)  and  a  high  proportion  of  extract  and  alcohol. 

At  the  proper  phase  beer  is  drawn  off  the  yeast  and  run  into 
casks,  where  it  undergoes  a  secondary  fermentation. 

Most  of  the  German  white  beers  are  produced  by  quick  top 
fermentation,  and  have  a  high  percentage  of  carbon  dioxide,  being 
bottled  before  the  second  fermentation  is  complete. 

Enghsh  ale  is  made  by  top  fermentation  of  a  wort  which  contains 
a  considerable  proportion  of  hops.  The  fermentation  is  checked 
at  an  early  stage,  hence  it  is  rich  in  sugar. 

Porter  is  a  dark  ale  made  from  brown  malt  dried  at  a  high  tem- 
perature. It  has  a  large  extract,  mainly  sugar,  and  may  contain 
caramel. 

Stout  is  porter  with  larger  alcohol  and  extract  contents. 

Detection  of  Ethyl  Alcohol. — Warm  10  c.c.  of  the  fluid  under 
test  with  a  few  drops  of  benzo^d  chloride ;  add  a  little  NaOH  solu- 
tion; ethyl  benzoate  is  formed  with  characteristic  odour  where  as 
little  as  o-i  per  cent,  alcohol  is  present.  Other  alcohols  produce 
ethers  with  characteristic  odours. 

The  Iodoform  Test. — ^Warm  10  c.c.  of  the  fluid  in  a  test-tube 


252  PRACTICAL  SAXITARY  SCIENCE 

with  a  few  drops  of  strong  solution  of  iodine  in  KI ;  add  solution  of 
NaOH  till  the  mixture  is  nearly  decolourized.  On  standing  a 
precipitate  of  iodoform  (star-shaped  or  hexagonal  tablet  crystals) 
forms  where  alcohol  is  present  to  the  extent  of  o"i  per  cent. 

Acetone,  lactic  acid,  and  certain  aldehydes  and  ketones,  give  this 
reaction,  but  not  pure  methyl  alcohol,  amyl  alcohol,  or  acetic 
acid. 


Fig.  66. — Estimation  of  Alcohol. 


Estimation  of  Alcohol.— Expel  free  CO.y  by  shaking  in  a  flask 
or  separator  funnel  and  drawing  the  still  liquid  away  from  the 
froth. 

Into  a  250  to  400  c.c.  flask  pour  100  c.c.  beer;  add  some  tannic 
acid  to  prevent  frothing:  dilute  to  about  150  c.c.  with  HoO  and 
distil.  All  the  alcohol  will  come  over  in  the  first  75  c.c.  distillate — 
i.e.,  three-fourths  the  original  measured  volume.  In  the  case  of 
liquors  high  in  alcohol,  it  is  better  to  distil  over  about  100  c.c. 
Make  up  the  distillate  to  the  volume  of  the  liquor  originally  taken 


ALCOHOLIC  J3  EVER  AGES  253 

and  shake  well.  Take  the  specific  gra,vity  in  a  pycnometcr.  Refer 
to  the  alcohol  table,  and  read  off  the  percentage  of  alcohol  by 
volume  or  by  weight. 

Tabarie'S  Method. — Find  the  specific  gravity  of  the  beer. 
Evaporate  100  c.c.  on  a  water-bath  to  one-fourth  the  volume. 
Make  up  to  the  original  volume  with  distilled  water,  and  find  the 
specific  gravity  of  the  dealcoholized  fluid.  Add  i  to  the  original 
specific  gravity,  and  from  the  sum  subtract  the  second  specific 
gravity.  The  difference  is  the  specific  gravity  corresponding  to 
the  alcohol  in  the  liquor.  Suppose  the  specific  gravity  of  the 
sample  to  be  I'gSgg,  and  that  of  the  dealcohohzed  sample  I'OogQ. 
Then  1-9899—  1-0099  =  0-9800  =  16-24  P^r  cent,  alcohol  by  volume. 

Acidity. — The  total  acidity  is  usually  expressed  in  terms  of 
lactic  acid.  Measure  20  c.c.  beer  and  free  it  from  CO2  by  raising 
it  to  the  boiling-point.  Cool,  and  titrate  with  y^  NaOH,  using 
litmus  as  indicator,     i  c.c.  ^^5-  NaOH  =  0-009  gramme  lactic  acid. 

The  Fixed  Acid  expressed  as  Lactic. — Evaporate  20  c.c.  beer  to 
one-fourth  its  volume,  dilute  with  water  to  original  volume;  titrate 
with  -f-ij  NaOH  as  before. 

Volatile  Acid  expressed  as  Acetic. — Distil  100  c.c.  beer  nearly 
to  dryness.  Should  the  residue  in  the  retort  be  still  acid,  add  some 
water  and  continue  the  distillation  to  dryness.  Now  titrate  the 
distillate  with  ~  NaOH,  each  cubic  centimetre  of  which  =  o-oo6 
gramme  acetic  acid.  The  normal  acidity  of  beer  is  due  to  CO2, 
acetic,  lactic,  malic,  and  other  organic  acids,  and  should  not  exceed 
in  100  c.c.  that  neutralized  by  30  c.c.  ^^  NaOH. 

The  Malt  Extract.— To  estimate  this  item  with  any  degree 
of  accuracy,  a  small  quantity  must  be  operated  on.  Take  5  c.c.  or 
5  grammes  in  a  large  platinum  dish  so  that  a  thin  film  is  formed  on 
the  bottom.  Dry  for  two  or  three  hours  on  the  water-bath,  and 
finish  the  drying  in  an  air-bath  at  a  temperature  somewhat  above 
100°  C. 

Bitters. — The  bitter  of  hops  is  readily  soluble  in  ether;  the  bitters 
of  quassia,  aloes,  and  hop  substitutes,  are  insoluble  in  ether;  whilst 
many  bitters  that  might  be  employed  are  soluble  in  ether,  the 
absence  of  a  bitter  taste  from  the  ether  extract  demonstrates  the 
absence  of  hops.  In  performing  the  test,  evaporate  the  beer  to  the 
consistence  of  a  syrup  before  extracting  with  ether.     Further,  lead 


254  PRACTICAL  SAXITARY  SCIENCE 

acetate  coniplctely  precipitates  the  bitter  material  of  hops,  but 
leaves  behind  some  of  the  bitters  of  hop  substitutes,  which  may 
be  recognized  on  concentrating  the  filtrate. 

Aloes. — Dry  200  c.c.  beer  and  treat  the  residue  with  ammonia. 
Filter,  cool,  and  treat  the  filtrate  with  HCl.  Collect  the  resin  on  a 
filter.  This  is  insoluble  in  cold  water,  ether,  petroleum  ether,  and 
chloroform,  but  soluble  in  alcohol.  It  has  a  characteristic  odour 
which  identifies  it. 

Gentian. — Treat  the  acid  residue  with  chloroform  in  the  cold:  no 
colour  is  produced;  warm,  and  a  camiine-red  colour  appears.  A 
small  quantity-  of  the  red  solution  mixed  with  a  drop  or  two  of 
ferric  chloride  solution  changes  to  a  greenish-brown. 

Qitassia. — Ouassiin  in  acid  solution  is  soluble  in  chloroform,  and, 
when  mixed  with  a  little  alcoholic  solution  of  ferric  chloride,  gives 
a  mahoganv-brown  coloration. 

Preservatives  in  Beer. — Boric  acid  and  salicylic  acid  are 
detected  in  the  same  manner  as  described  under  milk,  concentrating 
the  beer  if  necessar}^  to  one-fifth  or  one-tenth  of  the  bulk.  Sac- 
charin is  detected  by  acidulating  a  portion  with  H0SO4,  shaking 
with  a  mixture  of  equal  volumes  of  ether  and  petroleum  spirit, 
evaporating  down  with  a  little  NaOH  solution,  and  carefully 
heating  for  a  short  time  to  about  250°  C.  Salicyhc  acid  is  formed, 
and  this  is  tested  for  in  the  ordinary  way. 

Sulphurous  Acid. — To  25  grammes  sample  in  a  200  c.c.  flask  add 
25  c.c.  N-KOH.  Shake  and  set  aside  for  twenty  minutes.  Add 
10  c.c.  25  per  cent.  H2SO4  and  a  little  boiled  starch  solution. 
Titrate  rapidly  with  ^^ iodine  till  a  blue  colour  is  produced.  One  c.c. 
of  the  iodine  solution  =0-00064  gramme  SOo.  Sulphurous  acid  is 
used  to  regulate  the  fermentation  and  to  produce  a  flavour  of 
age. 

Sodium  Chloride. — Where  common  salt  has  been  added,  an 
allowance  not  exceeding  50  grains  per  gallon  must  be  made  for  the 
amount  of  this  compound  present  in  the  water,  malt,  and  hops 
used.  Ash  a  suitable  quantity  of  beer,  say  100  c.c;  exhaust  the 
ash  with  water;  titrate  the  solution  with  /^  AgNOg,  using  neutral 
potassium  chromate  as  indicator. 

Arsenic. — In  Lancashire  in  1900  an  outbreak  of  arsenical  poisoning 
occurred,  in  which  arsenic  amounting  to  --^^j  grain  per  gallon  was  fre- 


ALCOHOLIC  BEVERAGES  255 

quently  found,  and  it  was  stated  in  some  cases  that  i  grain  in  a  gallon 
was  found. 

Marsh  Test — Preliminary  Treatment  of  Beer.  —  Place  100  c.c. 
beer  freed  from  COg  by  shaking  in  a  porcelain  dish;  add  20  c.c. 
pure  concentrated  HNO3  and  3  c.c.  concentrated  H2SO4  ;  heat 
in  a  fume  chamber  till  vigorous  frothing  occurs;  lower  the  flame 
and  stir  till  frothing  ceases  ;  boil  freely  ;  continue  heating  till 
mass  chars  and  fumes  of  H2SO4  are  given  off;  pieces  of  filter-paper 
may  be  stirred  in  till  the  residue  is  dry;  cool,  add  50  c.c.  water,  and 
remove  masses  of  char  from  sides  of  dish  with  glass  rod ;  heat  to 
boiling  and  filter;  use  the  filtrate  in  the  Marsh  apparatus. 

Marsh  Apparatus. — Fit  up  a  generating  flask  with  funnel  tube. 
Attach  a  U-tube  containing  pumice  moistened  with  10  per  cent, 
lead  acetate  solution  to  absorb  H2S.  To  this  attach  a  CaCla  dr\'ing 
tube,  and  a  hard  glass  tube  of  about  6  millimetres  bore  drawn  out 
for  about  4  centimetres  to  i  millimetre  internal  diameter;  draw 
out  the  end  to  still  narrower  dimensions;  support  the  tube  over  a 
two-  or  three-burner  furnace,  wrapping  the  portion  in  contact  with 
the  flame  in  wire  gauze. 

Place  in  the  generating  flask  20  to  30  grammes  arsenic-free  stick 
zinc  and  a  perforated  platinum  disc  to  form  an  electric  couple. 
Run  in  through  the  funnel  sufficient  20  per  cent.  H2SO4  to  start 
the  reaction  and  expel  air.  When  aU  air  has  been  driven  out  and 
danger  of  explosion  has  passed,  heat  the  tube  to  bright  redness. 
When  absence  of  As  in  the  reagents  has  been  settled,  add  slowly 
through  the  funnel  the  solution  of  the  substance  in  20  per  cent. 
H2SO4.  When  the  flow  of  gas  begins  to  slacken,  add  some  30  per 
cent.  H2SO4,  and  later  40  per  cent,  acid,  tiU  all  As  has  been  ex- 
pelled. Two  or  three  hours  may  be  required  to  finish  the  expul- 
sion. If  no  mirror  forms  in  the  constriction  of  the  tube  in  an  hour, 
it  may  be  taken  that  there  is  no  As  present. 

If  more  than  o-i  milligramme  As  appears  to  be  present,  cut  off 
the  constriction  from  the  tube  and  weigh  it  on  a  fine  balance.  Dis- 
solve the  As  out  with  a  solution  of  sodium  hypochlorite ;  wash  the 
tube  with  water;  dry  with  alcohol  and  weigh.  The  loss  of  weight 
is  As. 

If  the  As  is  very  small  in  amount,  compare  the  mirror  with  a 
series  of  standard  mirrors  prepared  in  the  same  apparatus  from 


256  PRACTICAL  SAXITARY  SCIEXCE 

quantities  of  a  standard  solution  of  As  containing  from  0-005  to 
0-05  milligramme  As^Og.  Such  standard  solution  is  prepared  by 
dissolving  o-i  gramme  pure  As.,0.j  in  a  little  pure  NaOH  solution, 
acidifying  with  pure  H0SO4,  and  making  up  to  100  c.c.  with  water. 
Ten  c.c.  of  the  latter  fluid  is  further  made  up  to  i  litre.  One  c.c- 
=  0-0 1  milligramme  As.,0.}. 

Reinsch's  Test. — Acidify  100  c.c.  beer  with  i  c.c.  HCl  (free  from 
arsenic) ;  evaporate  to  less  than  half  the  bulk.  Set  up  two  beakers 
on  gauze  over  Bunsen  burners  (the  second  to  act  as  a  control).  In 
the  first  place  the  prepared  beer,  and  in  the  second  an  equal  volume 
of  water.  To  each  add  5  c.c.  concentrated  pure  HCl  and  a  strip 
of  bright  pure  copper-foil  10  millimetres  by  5  millimetres.  Heat 
for  an  hour,  replacing  from  time  to  time  the  water  lost  by  evapora- 
tion. If  a  deposit  forms  on  the  copper,  remove  it,  and  wash  very 
carefully  with  water,  alcohol,  and  ether.  Place  in  a  subliming 
tube  and  heat  over  a  low  flame.  The  crystals  are  for  the  most 
part  regular  octahedra,  with  perhaps  a  mixture  of  rectangular 
prisms. 

Clarke  has  made  this  test  quantitative :  Dissolve  the  arsenic  from 
the  Cu  slip  in  dilute  aqueous  solution  of  potash  and  H-.O^  in  the 
cold.  Then  boil,  and  filter  off  any  CuO.  Concentrate  the  filtrate 
to  a  small  bulk  and  wash  into  a  distilling  flask  with  strong  arsenic- 
free  HCl ;  add  some  ferrous  chloride ;  fit  the  flask  with  a  safety  tube 
and  connect  with  a  small  worm  condenser.  Distil  down  twice  with 
pure  strong  HCl.  Pass  H^S  into  the  distillate.  A  precipitate  will 
form  if  more  than  o-i  milligramme  be  present;  if  less  than  this 
quantitv,  a  3'ellow  colour.  As  little  as  o-ooi  milligramme  arsenic 
sulphide  gives  a  faint  yellow  colour,  which  may  be  matched  by  a 
series  of  standard  colours  produced  under  the  same  conditions.* 

Wine. 

In  making  wine  the  juice  of  the  grape  is  left  in  open  vats  where 
its  sugar  undergoes  spontaneous  fermentation.  The  bloom  which 
co\'ers  the  outside  of  the  grape  contains  the  necessary  yeast,  and  the 
natural  acidity  of  the  juice,  or  must,  excludes  foreign  organisms. 

*  See  description  of  Marsh-Berzelius  process,  Analyst,  February,  1902,  xxvii., 
48,  210. 


ALCOHOLIC  BEVERAGES  257 

The   relative   porportions   of   protein   and   sugar   influence   the 
character  of  the  wine,  as  yeast  {Saccharomyces  ellipsoideus)  Hves 
upon  the  protein,  and  sphts  the  sugar,  forming  alcohol  and  other 
products.     If  yeast  grow  in  little  sugar  and  much  protein,  it  can 
maintain  its  existence  until  all  the  sugar  is  changed;  such  a  wine 
is  said  to  be  dry  and  acid,  like  hock.     Conversely,  if  there  be  much 
sugar  and  little  protein,  the  growth  of  yeast  comes  to  an  end  before 
all  the  sugar  is  used,  and  that  left  behind  produces  a  sweet  wine. 
Intermediate   proportions  of  sugar   and   proteins   produce   corre- 
sponding results.     It  may  be  noted,  though,  that,  no  matter  what 
the  proportions  of  protein  and  sugar,  fermentation  cannot  proceed 
after  16  volumes  per  cent,  of  alcohol  have  appeared  in  the  liquid; 
this  is  why  a  natural  wine  can  never  contain  more  than  this  pro- 
portion of  alcohol.     Sherry  and  port  are  fortified  wines — that  is, 
containing,  as  they  do,  more  than  16  per  cent,  of  alcohol,  they 
have  the  difference  added  to  them.     Claret  and  hock  are  natural 
wines.     The  quality  of  wine  depends  on  the  species  of  yeast  used, 
the  variety  of  grape,  the  soil  and  climatic  conditions  of  growth  of 
the  grape,  and  the  mode  of  its  cultivation.     The  colour  of  red 
wines  is  produced  by  a  pigment  {cenocyanin)  residing  in  the  skins 
of  the  grapes,   which  is  turned   red  by  the   acids   present.      As 
alcohol  is  produced,  it  dissolves  out  this  pigment,  and  so  colours 
the  distillate.     Wine,  when  placed  in  casks,  undergoes  important 
changes:   water  evaporates  more  quickly  through  the  woodwork 
than  does  the  alcohol,  and  so  the  alcohol  becomes  concentrated. 
Further,  some  oxidation  of  the  tannic  acid  takes  place;  this  causes 
white  wines  to  be  somewhat  darker  in  colour,  and  red  wines  lighter, 
through  the  carrying  down  of  some  of  their  pigments  by  oxidized 
tannic  acid.     Frequently  a  small  amount  of  yeast  enters  the  cask, 
and  continues  the  fermentation,  thereby  increasing  the  quantity 
of  alcohol.     With  the  lapse  of  time,  some  of  the  alcohol  is  oxidized 
into  acetic  acid,  and  certain  compound  ethers  are  formed.     Wine 
in   bottles  adds   to   its   contained   ethers,    although   its   alcoholic 
strength  rarely,  if  ever,  increases.     It  is  an  error  to  suppose  that 
very  old  wine  contains  most  alcohol:  slow  oxidation  in  the  case  of 
wines,  as  in  all  other  organic  compounds,  produces  degeneration. 
It  is  more  than  probable  that  no  wine  improves  in  quality  after 
a  period  of  ten  to  fifteen  years. 

17 


25S  PRACTICAL  SANITARY  SCIENCE 

Fermentation  progresses  most  rapidly  at  a  temperature  between 
25°  and  30°  C,  but  finer  bouquet  is  produced  by  slower  fermenta- 
tion, and  accordingly  must  is  fermented  in  open  vats  in  cool  cellars 
at  5°  to  15°  C.  till  it  settles  out  comparatively  clear,  care  being 
taken  to  avoid  acetic  fermentation.  When  the  first  or  active 
fermentation  is  complete,  the  wine  is  drawn  off  into  casks,  where 
it  undergoes  a  second  slow  fermentation,  with  deposit  of  potassium 
bitartrate  and  development  of  the  characteristic  flavour.  The 
wine  is  sometimes  clarified  with  gelatin,  and  sometimes  pasteurized, 
before  the  final  bottling  or  casking.  Volatile  ethers  predominate 
in  natural  wines,  fixed  ethers  in  fortified.  Sparkling  wines,  as 
distinguished  from  still,  are  highl}^  charged  with  COg,  either  pro- 
duced naturally  by  after- fermentation  of  added  sugar  (champagne), 
or  artificially  b}^  carbonating,  as  in  the  case  of  soda-water. 

Port  wine  is  rich  in  tannin,  and  to  certain  inferior  wines  this 
astringent,  together  with  alum  and  catechu,  is  added.  Port  con- 
tains a  large  amount  of  extracts,  which  give  it  a  full  body,  and  old 
port  a  large  proportion  of  ethers,  of  which  (vmlike  sherry)  the 
fixed  ethers  predominate  over  the  volatile. 

Sherries,  as  imported  into  this  country,  are  all  fortified  and 
plastered,  and  contain  from  15  to  25  per  cent,  of  alcohol  b}'  weight. 
Old  sherry  contains  a  large  proportion  of  volatile  ethers,  and  to 
this  property  much  of  its  value  as  a  stimulant  must  be  attributed. 

Champagne  is  produced  from  black  grapes,  and  depends  for  its 
character  very  largely  upon  the  quality  of  the  grapes  of  a  particular 
vintage.  The  expressed  juice,  after  sedimentation  for  twelve  hours, 
is  drawn  off  and  fermented;  it  is  then  bottled  and  allowed  to  undergo 
secondary  fermentation  for  a  couple  of  3'ears,  during  which  time 
much  COo  is  produced,  and  a  deposit.  To  the  wine,  which  is  up 
till  now  sour,  cane-sugar,  which  has  been  dissolved  in  old  cham- 
pagne, is  added  in  varying  quantities.  Dry  champagnes  which 
find  their  way  to  England  contain  little  sugar — not  more  than  i  or 
2  per  cent.,  whilst  sweet  chcmipagnes  may  contain  10  to  15  per  cent. 

Claret  is  a  deep  red  wine,  somewhat  acid  and  astringent;  it  con- 
tains little  sugar,  but  considerable  quantities  of  volatile  ethers. 
Its  content  of  alcohol  varies  from  8  to  12  per  cent,  by  volume. 

Hock  is  a  white  wine  containing  little  sugar,  9  to  12  per  cent,  by 
volume  alcohol,  and  is  mildly  acid. 


ALCOHOLIC  BEVERAGES  259 

Plastering  is  the  term  applied  to  the  adulteration  of  the  must 
before  fermentation  with  plaster  of  Paris  or  gypsum,  wherein 
objectionable  potassium  sulphate  is  left  in  solution  in  the  wine: 

CaSOj  +  2KHC4HJO6  =  H2C4H4O6  +  CaC4H40f,  +  K.SO^. 

The  precipitation  of  calcium  tartrate  carries  down  impurities, 
the  colour  is  improved,  and  the  fermentation  hastened  and  made 
more  complete;  the  practice  is  said  to  enhance  the  keeping  qualities 
of  the  wine. 

Cane-sugar  is  added  to  the  must  to  increase  the  yield  of  alcohol. 
Glucose  is  used  instead  of  cane-sugar,  and  introduces  unfermentable 
matter,  dextrin,  and  various  mineral  salts. 

Added.  Water. — Gautier  ('  Traite  sur  la  Sophistication  et 
r Analyse  des  Vins  ')  has  shown  that  the  sum  of  the  weight  in 
grammes  of  alcohol  in  100  c.c.  and  total  acidity  (as  H2SO4)  in  a  litre 
varies  in  pure  wines  within  narrow  limits,  being  rarely  below  13  or 
above  17.  If  considerably  below  13,  water  may  be  assumed  to 
have  been  added. 

Colouring'  Matter  in  Wine.  —  Cubes  of  solid  transparent 
gelatin,  |  inch  square,  are  immersed  in  the  wine  for  twenty-four 
hours,  after  which  they  are  removed,  washed  in  water,  and  cut  in 
half.  In  genuine  wines  the  colouring  rnatter  will  not  have  pene- 
trated more  than  one-sixteenth  of  an  inch,  whilst  in  wines  coloured 
with  fuchsin,  cochineal,  logwood,  litmus,  indigo,  etc.,  the  cubes  will 
be  penetrated  to  the  centre.  The  colouring  matter  of  alkanet  root, 
turned  blue  b}^  ammonia,  is  the  only  foreign  matter  in  general  use 
which  slowly  penetrates  the  gelatin.  Dilute  ammonia  dissolves 
cochineal  and  logwood  out  of  the  gelatin,  the  cochineal  becoming 
purple  and  the  logwood  brown. 

Estimation  of  Alcohol.— iVs  in  beer. 

Acids. — The  acids  of  wine  are  chiefly  tartaric,  malic,  and  tannic, 
and  certain  acids  of  the  fatty  series — acetic,  formic,  etc. — produced 
during  fermentation.  Tartaric  acid  forms  with  potassium  a  bi- 
tartrate.  i\.s  alcohol  increases  in  wine  this  salt  becomes  less  soluble, 
and  finally  faUs  out  in  the  form  of  a  crust,  so  that  the  acidity 
diminishes  on  keeping.  Tannic  acid  is  obtained  from  the  skins 
and  stalks  of  the  grapes  used;  it  diminishes  by  oxidation  on  keeping, 
and  in  old  wines  is  small  in  amount. 


26o  PRACTICAL  SANITARY  SCIENCE 

Get  rid  of  CO.,  by  shaking.  Heat  about  20  c.c.  to  boiling,  and 
titrate  with  ^^  NaOH  (in  white  wines  and  cider  use  phenol- 
phthalein  as  indicator).  One  c.c.  ^xr  NaOH  =  0-0067  gramme  mahc 
acid,  or  0-0075  gramme  tartaric  acid.     This  is  the  total  acidity. 

Volatile  Acids. — Place  50  c.c  with  a  little  tannin  in  a  distilling 
flask  connected  with  a  condenser.  Connect  a  second  distilling 
flask  containing  250  c.c.  water  with  the  first  by  glass  tube  passing 
almost  to  the  bottom.  Heat  both  to  boiling:  then  lower  the  flame 
under  the  distilling  flask  and  pass  steam  through  the  wine  until 
200  c.c.  distillate  come  over.  Titrate  the  distillate  with  -^^  NaOH 
(indicator  phenolphthalein).  One  c.c.  y\  NaOH  =0-006  gramme 
acetic  acid. 

Ethers. — Ethers  are  produced  in  wines  by  the  chemical  action 
which  takes  place  between  the  acids  and  alcohols.  Volatile  ethers 
are  obtained  from  volatile  acids,  such  as  acetic,  and  these,  especially 
acetic  ether,  predominate  in  natural  wines.  Fixed  ethers  are 
derived  from  fixed  acids,  such  as  tartaric,  and  are  found  in  forti- 
fied wines:  they  impart  to  wine  its  bouquet.  CEnanthic  ether 
I  part  in  50,000  wine  imparts  the  vinous  smell  and  taste  to  all 
wines  in  common. 

Extract.  —  Dry  10  grammes  to  constant  weight  in  a  platinum 
dish:  a  small  amount  of  glycerin  may  be  lost. 

Ash. — Ignite  the  dried  residue  at  a  low  temperature  and  weigh. 
Most  natural  wines  contain  i  part  ash  to  10  parts  extract. 

Sug'ars.  —  The  chief  sugar  of  wine  is  laevulose,  of  which  a 
natural  wine  should  not  contain  more  than  0-5  per  cent.  Fortified 
wines  mav  contain  from  2  to  25  per  cent.  Extractives  found  in 
wine  consist  of  gums  and  various  carbohydrates,  and  contribute  to 
the  taste  and  so-called  body  of  the  wine.  Reducing  sugars  are 
determined  by  Fehling's  method. 

Potassium  Sulphate. — Acidify  100  c.c.  of  the  wine  with  HCl; 
boil  and  add  excess  BaCU.  Filter,  wash  well,  dry,  ignite,  weigh  as 
BaS04:  calculate  the  equivalent  K0SO4.  More  than  0-06  gramme 
indicates  plastering. 


ALCOHOLIC  BEVERAGES  261 


Spirits. 


Spirits. — Whisky,  brandy,  rum,  gin,  etc. 

Whisky. — Whisky  is  made  from  malt  or  malt  and  grain,  and 
distilled  in  pot-stills  or  patent-stills.  For  many  years  superior 
claims  were  made  for  the  pot-still  article,  but  these  claims  have 
been  destroyed  by  the  report  of  the  recent  Royal  Commission. 

In  1905  a  London  magisterial  investigation  decided  that  patent- 
still  spirit  alone  is  not  whisky,  and  that  whisky  cannot  be  made 
from  maize ;  the  above  report  upsets  this  view. 

The  pot-still  in  its  simplest  form  is  a  pot  with  a  long  neck  over 
which  the  distilled  alcohol  passes  when  the  wash  or  fermented 
mash  of  grain  is  boiled.  Usually  two  distillations  are  carried  out 
in  producing  Scotch  whisky. 

The  patent-still  is  an  arrangement  of  pipes  and  chambers  through 
which  steam  is  passed  continuously  as  the  wash  distils.  This  is  a 
cheaper  process  capable  of  a  much  greater  output. 

The  Commission  concluded  that  it  would  be  no  advantage  to  pro- 
hibit the  use  of  foreign  barley,  and  it  would  be  too  arbitrary  to  say 
that  Scotch  whisky  should  be  made  from  malt  alone,  and  Irish  from 
a  mixture.  Maize  affects  the  flavour,  but  there  is  no  valid  reason 
for  excluding  it.  Patent-still  whiskies  are  less  varied  than  pot-still, 
but  the  same  effects  are  produced  by  both  kinds  if  taken  in  the 
same  quantity  and  in  the  same  strength. 

Pot-still  distillers  admit  the  need  of  blending  with  patent-still 
whisky,  unless  their  own  spirit  can  be  matured  longer;  patent-still 
tones  down  the  pungent  taste  of  the  other.  Cheap  blends  contain 
as  little  as  10  per  cent,  of  pot-still.  As  whiskies  used  in  England 
are  usually  blends,  and  as  the  patent-still  is  adapted  for  economical 
and  larger  production,  and  as  there  is  no  evidence  that  the  form 
of  still  has  any  relation  to  the  wholesomeness  of  the  spirit,  the 
Commission  could  not  recommend  that  the  term  '  whisky  '  should 
be  restricted  to  the  pot-still  variety. 

Brandy  is  determined  by  the  report  as  a  potable  spirit  made  from 
fermented  grape-juice  and  from  no  other  materials.  '  British 
brandy  '  is  defined  as  a  compounded  spirit  prepared  by  a  rectifier 
or  compounder  by  redistilling  duty-paid  spirits  made  from  grain 
with  flavouring  ingredients,  or  by  adding  flavouring  materials  to 


262  PRACTICAL  SAXITARY  SCIEXCE 

such  .spirits;  the  nature  of  the  flavouring  materials  is  not  dis- 
closed. 

True  brandy  is  distilled  wine,  and  was  originally  procured  from 
a  rich  Cognac  district  in  France.  Its  quality  varies  with  the 
character  of  the  grapes  used,  the  best  grapes  yielding  grande 
champagne,  a  genuine  liqueur  brandy.  It  is  to  be  feared  that 
little  of  the  brandy  sold  in  this  country  is  so  derived.  Brandy 
contains,  beside  ethyl  alcohol,  volatile  ethers  in  large  amount, 
an  important  distinction  from  whisky.  Its  percentage  of  alcohol 
is  about  the  same  as  that  of  whisky. 

Alcohol. — Estimation  by  distillation  as  under  Beer. 

Metallic  Impurities. — Pb,  Cu,  etc.  Detection  and  estimation  as 
under  Water. 

Fusel-Oil. — Fusel-oil  is  the  most  important  impurity  of  spirit. 
It  is  more  injurious  than  ordinary  alcohol,  and  should  not  be 
permitted  to  exceed  o-2  per  cent,  (i)  Shake  20  c.c.  of  the  spirit 
with  2  c.c.  dilute  KOH.  Evaporate  on  water-bath  to  2  or  3  c.c. 
Cool  and  add  5  c.c.  strong  sulphuric  acid.  The  odours  of  valerianic 
and  butyric  acids  will  be  detected  if  fusel-oil  be  present.  (2)  Distil 
off  four-fifths  of  the  sample,  and  extract  the  residue  with  ether: 
allow  the  extract  to  evaporate  spontaneousl}',  and  treat  what  is 
left  with  H2SO4  and  sodium  acetate:  the  odour  of  pear  is  emitted. 
(3)  Evaporate  50  c.c.  slowh'  over  a  steam-bath;  carefully  smell 
the  remainder  for  traces  of  fusel-oil.  (4)  Decolourize  a  portion  of 
the  sample  with  animal  charcoal  and  add  a  few  drops  each  of  h3^dro- 
chloric  acid  and  colourless  aniline-oil.  In  the  presence  of  fusel-oil 
a  rose  tint  is  produced  in  the  aniline-oil. 

[Tests  for  methylated  spirit:  (i)  Odour:  (2)  a  weak  solution 
of  sodium  nitroprusside  (i  per  cent.)  and  ammonia,  added  to  a 
mixture  containing  methylated  spirit,  give  a  red  colour  within 
ten  or  fifteen  minutes.] 

Estimation — Marquardt  Method.— Jo  100  c.c.  spirit  add  20  c.c. 
-^;  NaOH,  and  saponify  by  allowing  to  stand  overnight,  or  by  boiling 
for  an  hour  under  a  reflux  condenser.  Distil  90  c.c. ;  add  25  c.c. 
water,  and  distil  an  additional  25  c.c.  Saturate  the  distillate  with 
NaCl,  and  add  saturated  NaCl  solution  till  specific  gravity  is  i-i. 
Extract  the  salt  solution  four  times  with  CCI4  (recently  purified  by 
boihng  with  sulphuric  acid  and  potassium  bichromate,  and  distilling) 


ALCOHOLIC  BEVERAGES  263 

using  40,  30,  20,  and  10  c.c,  respectively.  Wasli  the  CCI4  extract 
three  times  with  50  c.c.  portions  of  a  saturated  Na('l  solution,  and 
twice  with  the  same  volumes  of  saturated  sodium  sulphate  solution. 
Now  boil  the  tetrachloride  for  eight  hours  with  5  c.c.  concentrated 
H2SO4,  5  grammes  potassium  bichromate,  and  45  c.c.  water  under 
a  reflux  condenser.  Add  30  c.c.  water,  and  distil  till  about  20  c.c. 
remain;  add  80  c.c.  water,  and  distil  till  5  c.c.  are  left. 

Neutralize  the  distillate  to  methyl  orange;  add  phenolphthalein, 
and  run  in  /o  NaOH  till  neutral.  One  c.c.  -^-^  NaOH=o-oo88 
gramme  amyl  alcohol.  In  the  oxidation  and  second  distillation 
the  corks  used  should  be  covered  with  tinfoil. 

Rose's  Method. — Chloroform  quickly  removes  fusel-oil  from 
dilute  spirit,  and  the  presence  of  fusel-oil  in  chloroform  increases 
the  capacity  of  the  latter  for  dissolving  ethylic  alcohol.  So,  there- 
fore, if  chloroform  be  shaken  with  dilute  ethyl  alcohol  containing 
fusel-oil,  its  volume  will  be  considerably  greater  than  when  shaken 
with  the  same  volume  of  pure  ethyl  alcohol. 

Dilute  the  spirit  to  be  tested  until  its  specific  gravity  is  0-9655 
at  15°  C.  (30  per  cent,  alcohol  by  volume).  If  the  sample  is  weaker 
than  this  it  must  be  fortified  by  absolute  alcohol  (i  per  cent,  error 
+  or  -  corresponds  with  o-oigg  per  cent,  by  volume  of  fusel-oil). 
In  the  special  tube  place  20  c.c.  chloroform,  which  at  15°  C.  reaches 
the  lower  division  of  the  scale.  Add  100  c.c.  alcohol  and  i  c.c. 
H2SO4,  specific  gravity  1-2857.  Stopper  the  apparatus  and  shake 
a  definite  number  of  times,  say  150.  Let  stand  for  some  time,  and 
read  the  volume  of  chloroform.  Submit  pure  alcohol  of  the  same 
strength  to  the  same  process,  and  note  the  difference  in  volume  of 
the  chloroform.  An  increase  o-oi  c.c.  (the  scale  is  readable  to 
o-oi  c.c.)  is  equal  to  0-006631  per  cent,  amyl  alcohol. 

Methyl  Alcohol — Method  of  Riche  and  Bardy. — This  method 
depends  on  the  formation  of  methyl-anilin-violet.  To  10  c.c. 
sample  add  15  grammes  iodine  and  2  grammes  amorphous  phos- 
phorus. Stand  in  iced  water  till  action  has  ceased.  Distil  on  a 
water-bath  the  methyl  and  ethyl  iodides  into  30  c.c.  water.  Wash 
with  dilute  NaOH  to  remove  free  iodine.  Separate  the  heavy  oily 
liquid  which  settles,  and  mix  with  5  c.c.  anilin  in  a  flask  placed  in 
cold  water.  After  an  hour  boil  and  add  about  20  c.c.  15  per  cent, 
soda  solution.     The  bases  rise  to  the  top  as  an  oily  layer;  float 


264  PRACTICAL  SANITARY  SCIENCE 

them  up  with  water  and  pipette  off.  Oxidize  i  c.c.  of  the  oily 
liquid  by  heating  in  a  glass  tube  at  90  °C.  for  eight  or  ten  hours 
with  2  parts  NaCl,  3  parts  Cu(N0.,)2,  and  100  parts  clean  sand. 
Exhaust  with  warm  alcohol,  filter,  and  make  up  to  100  c.c.  with 
alcohol.  In  the  case  of  pure  spirits  the  liquid  is  red,  but  in  the 
presence  of  i  per  cent,  methyl  alcohol  it  is  violet.  Dilute  5  c.c.  of 
the  coloured  liquid  to  100  c.c.  with  water,  and  dilute  5  c.c.  of  this 
again  to  400  c.c.  Heat  the  liquid  in  a  porcelain  dish  with  some 
pure  white  merino  wool  (free  from  sulphur)  for  half  an  hour.  If 
the  spirits  be  pure  the  wool  will  remain  white,  but  if  methylated 
the  fibre  will  become  violet.  A  quantitative  estimation  can  be 
made  by  comparing  the  tint  with  a  set  of  standards  containing 
known  percentages  of  methylic  alcohol. 

Rum  is  prepared  from  molasses,  a  by-product  in  the  manufac- 
ture of  sugar,  but  the  best  varieties  are  obtained  by  fermenting  the 
juice  of  the  sugar-cane.  One  by-product — ethyl  butj^rate — confers 
upon  it  its  characteristic  flavour.  Like  brandy,  however,  much 
of  the  rum  sold  in  this  country  is  made  from  silent  spirit,  flavoured 
with  characteristic  bj^-products. 

Gin  is  prepared  by  distilling  and  redistilling  a  mixture  of  vyo.  and 
malt.  In  the  last  distillation  juniper  berries,  salt,  and  hops,  are 
added,  and  the  product  is  run  off  into  cisterns  lined  with  white 
tiles,  whereby  colouring  matters  are  prevented  entering  the  spirit. 
The  best  gins  are  distilled  in  Holland;  but  much  of  the  gin  of 
commerce  is  concocted  from  silent  spirit,  resins,  and  juniper  berries. 

The  term  '  proof-spirit  '  is  applied  to  a  mixture  of  57-06  per  cent, 
by  volume  of  absolute  alcohol  in  water.  It  has  a  specific  gravity 
of  919-8  at  15°  C. 

Brandy,  whisky,  and  rum,  may  be  25  degrees  under  proof — that 
is,  may  contain  75  per  cent,  of  the  alcohol  found  in  proof-spirit. 
Gin  may  be  35  degrees  under  proof — that  is,  may  contain  65  per 
cent,  of  the  alcohol  found  in  proof-spirit. 

Spirits  generally  contain  40  to  60  per  cent,  of  alcohol;  wines 
8  to  16;  beers  5  to  7. 

Acidity  of  Spirits. — Titrate  with  decinormal  alkali  and  calculate 
as  acetic  acid.     One  c.c.  y    alkali  =  o -006  gramme  acetic  acid. 

Esters. — Dilute  250  c.c.  of  the  spirit  with  50  c.c,  water,  and  distil 
200  c.c.    Neutralize  50  c.c.  of  the  distillate  with  decinormal  alkali 


ALCOHOLIC  BEVERAGES 


265 


(phenolphthalein  indicator);  add  yg-  alkali  in  considerable  excess. 
Boil  for  an  hour  under  a  reflux  condenser.  Cool  and  titrate  with  -^^ 
alkah.  The  number  of  cubic  centimetres  -/i;  alkali  used  in  the 
saponification  multiplied  by  o' 0088=^  grammes  esters  calculated  as 
ethyl  acetate. 

Fupfupal. — Prepare  a  standard  furfural  solution.  Dissolve 
I  gramme  redistilled  furfural  in  100  c.c.  95  per  cent,  alcohol. 
Dilute  I  c.c.  of  this  to  100  c.c.  with  50  per  cent,  alcohol.  One  c.c. 
==  O'oooi  gramme  furfural.  Dilute  20  c.c.  of  the  above  distillate  to 
50  c.c.  with  50  per  cent,  alcohol  free  from  furfural.  Add  2  c.c. 
colourless  anilin  and  0-5  c.c.  HCl,  specific  gravity  1-125.  Make 
standards,  from  which  match  the  tint. 

Furfural  is  found  in  pot-still,  but  not  in  patent-still,  spirit. 


Alcohol  Table. 


Sp.  Gr.  at 

Per  Cent, 

Per  Cent. 

Sp.  Gr.  at 

Per  Cent. 

Vc. 

Alcohol  (Vol.). 

under  Proof. 

15°  c. 

Alcohol  (Vol.). 

I'OOO 

0-00 

100-00 

0-973 

23-10 

0-999 

0-66 

g8-84 

0-972 

24-08 

o-ggS 

1-34 

97-66 

o-g7i 

25-07 

0-997 

2-12 

96-29 

o-g70 

26-04 

0-996 

2-86 

95-00 

o-g6g 

26-95 

0-995 

3-55 

93-78 

o-g68 

27-86 

0-994 

4-27 

92-50 

o-g67 

28-77 

0-993 

5-00 

91-23 

0-966 

29-67 

0'9g2 

5-78 

89-87 

0-965 

30-57 

0-99I 

6-55 

88-50 

0-964 

31-40 

o-ggo 

7-32 

87-16 

0-963 

32-19 

0-989 

8-i8 

85-65 

0-962 

32-98 

0-988 

9-04 

84-15 

o-g6i 

33-81 

0-987 

9-86 

82-70 

0-960 

34-54 

o-g86 

IO-73 

81-20 

0-959 

35-28 

o-g85 

ii-6i 

79-65 

0-958 

36-04 

o-g84 

12-49 

78-10 

0-957 

36-70 

0-983 

13-43 

76-46 

0-956 

37-34 

o-g82 

14-37 

74-82 

0-955 

38-04 

o-g8i 

15-30 

73-18 

0-954 

38-75 

o-g8o 

16-24 

71-54 

0-953 

39-47 

o-gyg 

17-17 

69-90 

0-952 

40-14 

o-gyS 

18-25 

68-00 

0-951 

40-79 

o-g77 

19-28 

66-20 

0-950 

41-32 

0-976 

20-24 

64-53 

0-949 

41-84 

0-975 

2i-ig 

62-87 

0-948 

42-40 

0-974 

22-18 

61-13 

0-947 

42-95 

Per  Cent. 
under  Proof. 


59-52 
57-80 
56-06 
54-37 
52-77 
51-18 
49-60 
48-00 
46-44 
44-97 
43-60 
42-20 
40-74 

39-47 
38-18 
36-83 
35-68 
34'57 
33-32 
32-08 
30-84 
29-66 
28-52 
27-60 
26-67 
25-70 
24-74 


266 


PRACTICAL  SANITARY  SCIENCE 
Alcohol  IdihlQ— continued. 


Sp.  Or.  at 

Per  Cent. 

Per  Cent. 

Sp.  Gr.  at 

Per  Cent. 

Per  Cent. 

IS"  c. 

Alcohol  (Vol.). 

•inder  Proof. 

Vc. 

Alcohol  (Vol.). 

over  Proof. 

0-946 

43-5<J 

23-66 

0-899 

66-25 

I6-II 

0-945 

44-iS 

22-58 

0-89S 

66-69 

16-88 

0-944 

44-79 

21-50 

0-897 

67-11 

17-61 

0-943 

45-41 

20-43 

0-896 

67-53 

18-34 

0-942 

46-02 

19-36 

0-895 

67-93 

19-05 

0-941 

46-59 

18-36 

0-894 

68-33 

19-74 

0-940 

47-13 

17-40 

0-893 

68-72 

20-42 

0-939 

47-67 

16-46 

0-892 

69-11 

2I-II 

0-93S 

48-21 

15-50 

0-891 

69-50 

21-79 

0-937 

48-75 

14-57 

0-890 

69-92 

22-53 

0-936 

49-29 

13-63 

0-889 

70-35 

23-29 

0-935 

49-81 

12-70 

0-888 

70-77 

24-02 

0-934 

50-31 

11-82 

0-887 

71-17 

24-73 

0-933 

50-82 

10-94 

0-886 

71-58 

25-44 

0-932 

51-32 

10-05 

0-885 

71-98 

26-15 

0-931 

51-82 

9-20 

0-884 

72-38 

26-85 

0-930 

52-29 

8-36 

0-883 

72-77 

27-52 

0-929 

52-77 

7-52 

0-882 

73-15 

28-19 

0-92S 

52-24 

6-70 

j       0-881 

73-54 

28-87 

0-927 

53-72 

5-86 

0-880 

73-93 

29-57 

0-926 

54-19 

5-03 

0-879 

74-33 

30-26 

0-925 

54-66 

4-20 

0-878 

74-70 

30-92 

0-924 

55-13 

3-38 

0-877 

75-08 

31-58 

0-923 

55-60 

2-56 

0-876 

75-45 

32-23 

0-922 

56-07 

1-74 

0.875 

75-83 

32-89 

0-921 

56-54 

0-92 

0-874 

76-20 

33-54 

0-920 

56-98 

0-14 

0-873 

76-57 

34-19 

0-9198 

57-06 

Proof 

0-872 

76-94 

34-84 

Per  Cent. 

0-871 

77-29 

34-45 

over  Proof, 

0-870 

77-64 

36-07 

0-919 

57-45 

0-68 

0-869 

78-00 

36-69 

0-918 

57-92 

I-5I 

0-868 

78-36 

37-33 

0-917 

58-36 

2-28 

0-867 

78-73 

37-98 

0-916 

58-80 

3-05 

0-866 

79-12 

38-65 

0-915 

59-22 

3-78 

0-865 

79-50 

39-32 

0-914 

59-63 

4-50 

0-864 

79-86 

39-96 

0-913 

60-07 

5-27 

0-863 

80-22 

40-60 

0-912 

60-52 

6-07 

0-862 

8o-6o 

41-26 

0-91 1 

60-97 

6-86 

0-86I 

81-00 

41-96 

0-910 

61-40 

7-61 

0-860 

81-40 

42-66 

0-909 

61-84 

8-37 

0-859 

81-80 

43-35 

0-908 

62-31 

9-20 

0-858 

82-19 

44-04 

0-907 

62-79 

10-03 

0-857 

82-54 

44-66 

0-906 

63-24 

10-84 

0-856 

82-90 

45.28 

0-905 

63-69 

11-64 

0-855 

83-25 

45-90 

0-904 

64-14 

12-41 

0-854 

83-60 

46-51 

0-903 

64-58 

13-18 

0-853 

83-94 

47-11 

0-902 

65-01 

13-92 

0-852 

84-27 

47.70 

0-901 

65-41 

14-62 

0-851 

84-60 

48.27 

0-900       1 

65-81 

I5'33 

0-850 

84-93 

48-84 

A  LCOHOLIC  Hli  VE  RAG  IIS 
Alcohol  T2i\i\Q— continued . 


'267 


Sp.  Gr.  at 

Per  Cent. 

Per  Cent. 

Sp.  Gr.  at 

Per  Cent. 

Per  Cent. 

15°  C. 

Alcohol  (Vol.). 
85-26 

over  Proof. 

15°  C. 

Alcohol  (Vol.). 

over  Proof. 

0-849 

49-38 

0-820 

94-00 

64-74 

0-848 

85-59 

50-00 

0-819 

94-26 

65-18 

0-847 

85-94 

50-61 

o-SiS 

94-51 

65-62 

0-846 

86-28 

51-21 

0-817 

94-76 

66-07 

0-845 

86-61 

51-78 

o-8i6 

95-03 

66-53 

0-844 

86-93 

52-34 

0-815 

95-29 

67-00 

0-843 

87-24 

52-90 

0-814 

95-55 

67-46 

0-842 

87-55 

53-43 

o-8i  ^, 

95-82 

67-92 

0-841 

87-85 

53-96 

0-812 

96-08 

68-38 

0-840 

88-16 

54-50 

0-81 1 

96-32 

68-80 

0-839 

88-46 

55-02 

o-8io 

96-55 

69-20 

0-838 

88-76 

55-55 

0-809 

96-78 

69-61 

0-837 

89-08 

56-10 

o-8o8 

97-02 

70-03 

0-836 

89-39 

56-66 

0-807 

97-27 

70-46 

0-835 

89-70 

57-20 

0-806 

97-51 

70-88 

0-834 

89-99 

57-71 

0-805 

97-73 

71-26 

0-833 

90-29 

58-23 

0-804 

97-94 

71-64 

0-832 

90-58 

58-74 

0-803 

98-16 

72-02 

0-831 

90-88 

59-26 

0-802 

98-37 

72-40 

0-830 

91-17 

59-77 

0-801 

98-59 

72-77 

0-829 

91-46 

60-28 

0-800 

98-80 

73-14 

0-828 

91-75 

60-79 

0-799 

98-98 

73-47 

0-827 

92-05 

61-32 

0-798 

99-16 

73-81 

0-826 

92-36 

61-86 

0-797 

99-35 

74-14 

0-825 

92-66 

62-38 

0-796 

99-55 

74-50 

0-824 

92-94 

62-88 

0-795 

99-75 

74-83 

0-823 

93-23 

63-38 

0-794 

99-96 

75-18 

0-822 

93-49 

63-84 

0-7938 

100-00 

75-25 

0-82I 

93-75 

64-30 

OTHER  FOODSTUFFS. 

Lime  and  Lemon  Juices.  —  The  Board  of  Trade  requires 
that  these  juices  shall  have  a  specific  gravity  of  1-030,  and  shall 
have  acidity  of  6-8  per  cent,  citric  acid.  The  specific  gravity  is 
determined  in  the  usual  manner;  and  the  free  acidity  by  titration 
with  Yo  soda  (i  c.c.  =  0-007  gramme  citric  acid).  Where  sulphuric 
or  other  mineral  acid  is  added  as  an  adulterant,  it  is  estimated  in 
the  usual  way.  These  juices  are  generally  fortified  with  3  to  4  per 
cent,  of  alcohol. 

Adulterants. — Tartaric  acid,  mineral  acids,  glucose,  cane-sugar, 
invert-sugar,  preservatives,  coal-tar  dyes.  With  the  exception  of 
tartaric  acid,  determine  each  of  these  in  the  usual  manner. 


268  PRACTICAL  SANITARY  SCIENCE 

Tartaric  Acid. — Mix  20  grammes  of  juice  with  5  grammes  KCl; 
neutralize  with  KOH,  and  make  up  to  50  c.c.  with  water.  Add 
5  grammes  citric  acid,  stir  the  solution,  and  stand  overnight. 
Wash"  the  precipitated  acid  potassium  tartrate  with  a  saturated  ■ 
solution  of  acid  potassium  tartrate,  and  afterwards  two  or  three 
times  with  10  per  cent.  KCl.  Titrate  hot  with  -^^  NaOH  (i  c.c. 
=  0-0075  gramme  tartaric  acid.) 

Estimation  of  Citric  Acid — Warrington's  Method. — Neutralize 
15  to  20  c.c.  ordinary  juice,  or  3  to  4  c.c.  concentrated  juice, 
with  normal  soda,  and  make  up  to  about  50  c.c.  Heat  on  a 
water-bath,  and  add  CaCU  until  slightly  in  excess  of  the  organic 
acids  present.  Boil  for  half  an  hour,  filter,  and  wash  the  pre- 
cipitate with  hot  water.  Concentrate  the  filtrate  and  washings 
to  about  15  c.c.  and  add  a  drop  of  ammonia,  which  produces  a 
further  precipitate.  Collect  this  on  a  small  filter  with  the  assist- 
ance of  the  previous  filtrate ;  wash  with  a  small  quantity  of  hot  water. 
Dry  both  precipitates;  ignite  at  a  low  red  heat,  and  titrate  the  ash 
with  ^  acid  (i  c.c.  =  0'007  gramme  Hg-Ci.HoO). 

Vineg^aP. — Malt  vinegar,  as  distinguished  from  wood  vinegar 
(acetic  acid  and  water),  is  made  by  soaking  malt  or  malt  and  barley 
in  successive  quantities  of  hot  water  until  the  extraction  is  com- 
plete, fermenting  the  extract  with  yeast,  and  finally  pumping  the 
fermenting  mass  over  wickerwork  coated  with  Mycodernia  aceti  by 
which  the  alcohol  is  converted  into  acetic  acid.  Other  bodies, 
such  as  aldehydes,  acetic  ether,  etc.,  are  formed  at  the  same  time. 

Specific  Gmu//y.— Determine  in  the  usual  way;  specific  gravity 
should  be  about  1-019. 

Acetic  Acid. — Dilute  10  c.c.  to  50  c.c.  and  titrate  with  -f^j  NaOH 
(phenolphthalein  as  indicator),  (i  c.c.  /„  NaOH  =  o-oo6  gramme 
acetic  acid.) 

Nitrogen. — Operate  on  25  c.c.  by  the  Kjeldahl  process. 

Phosphoric  Acid. — Operate  on  25  c.c.  by  Neumann's  method. 

Sulphuric  Acid. — When  the  ash  of  vinegar  fails  to  be  alkaline, 
mineral  acid  has  been  added.  Evaporate  50  c.c,  of  the  sample  to 
dryness  with  25  c.c.  -^  NaOH,  and  ignite  at  lowest  possible  tem- 
perature. Add  25  c.c.  -^^  HCl,  heat  to  expel  CO,,  and  filter;  wash 
with  hot  water,  and  collect  washings,  and  filtrate.  Titrate  the 
free  acid  with  /^  NaOH  and  phenolphthalein  (i  c.c.  j^  NaOH 
=  0-0049  gramme  H^SOj). 


MUSTARD  269 

Total  Solids. — Evaporate  25  c.c.  to  constant  weight.  Ignite  the 
residue  at  a  low  temperature  to  obtain  the  ash. 

A  good  malt  vinegar  contains  roughly  5-5  per  cent,  acetic  acid, 
2'5  per  cent  extract,  0-5  per  cent,  ash,  0-075  per  cent.  PgOg,  0-075 
per  cent.  N,  and  has  a  specific  gravity  of  1-020. 

Mustard. — Mustard  is  derived  from  the  seeds  of  the  black  and 
white  mustard  plants  {Brassica  nigra  and  alba).  A  little  turmeric 
and  coal-tar  colours  are  usually  added  to  the  ground  seeds,  and 
sometimes  foreign  starches  and  ground  chillies  (small  pods  of 
Cayenne  pepper).  These  adulterants  are  all  harmless.  Starch  is 
readily  detected  by  the  iodine  test.  Turmeric  becomes  brownish- 
red  under  the  action  of  ammonia.  White  mustard  is  recognised 
under  the  microscope  by  the  hexagonal  or  '  infundibuliform  '  cells 


Fig.  67. — Cells  of  Cuticle  of  Mustard. 

of  the  cuticle,  possessing  a  central  ostium  occupied  by  the  so-called 
'  mucilage '  cells. 

Mustard  oil  is  a  slightly  yellow  refractive  liquid  of  strong  odour. 
It  boils  between  148°  and  156°  C,  and  has  a  specific  gravity  varying 
between  1-020  and  1-030.  Colour  changes  to  reddish-brown  on 
exposure  to  light.  Volatile  oil  of  black  mustard  interacts  with 
ammonia  to  form  thiosinamine : 

NH3  +  C3H5CNS=  CS.NH2.NH.C3H5. 

The  oil  is  estimated  by  extracting  with  ether  in  a  Soxhlet's 
apparatus.     Good  samples  contain  about  30  per  cent.  oil. 

Pepper.  —  Black  pepper  is  derived  from  the  unripe  berries  of 
Piper  nigrum,  and  white  pepper  from  the  ripe  fruit.  A  transverse 
section  of  a  black-pepper  berry  presents  an  external  layer  of  cells, 
somewhat  resembling  bean  starch  granules,  within    these  a  la^-e^ 


2  70  PRACTICAL  SANITARY  SCIENCE 

of  elongated  cells  arranged  transversely  to  the  foregoing,  next  a 
reticulum  containing  oil  globules,  more  internally  still  a  layer  of 
flask-shaped  cells,  and  finally  a  central  mass  of  angular  cells  con- 
taining starch. 

Pepper  is  largely  adulterated,  but  with  substances  which  are 
harmless.  These  are  various  foreign  starches,  palm-nut  powder^ 
ground  stones  of  olives,  ground  shells  of  walnuts,  and  occasionall}' 
chalk,  clay,  and  brick-dust. 


Fig.  68. — Black  Pepper,      x  30. 

The  ash  of  black  pepper  should  not  exceed  6' 5  per  cent., 
and  that  of  white  pepper  should  not  exceed  3-5  per  cent.  In 
microscopically  examining  pepper,  it  must  be  remembered  that, 
unlike  mustard,  pepper  naturally  contains  starch. 

Sug^ar. — Glucose  (dextrose)  or  grape-sugar,  and  fructose  (laevu- 
lose)  occur  in  grapes  and  other  fruits,  together  with  sucrose  (cane- 
sugar). 

Cane-sugar  probably  develops  first,  and  afterwards  gives  origin 
to  the  other  two ;  this  change  is  readily  produced  by  hydrolysis : 

HoO  +  Ci2Ho20ii=  CgHiaOelglucose)  -1-  CgHi206(fructose). 


SUGAR  271 

Cane-sugar  is  widely  distributed  in  the  vegetable  kingdom.  It 
forms  one  of  the  most  important  foodstuffs.  Little  chemical  energy 
is  required  to  convert  it  into  glucose  (the  final  form  of  digested 
carbohydrates)  compared  with  that  necessary  to  transform  starches. 

Inasmuch  as  all  carbohydrates  must  pass  into  the  form  of  glucose 
before  they  can  be  utilized  in  the  cell,  and  inasmuch  as  the  greater 
portion  of  the  kinetic  energy  of  the  body  is  liberated  in  the  combus- 
tion of  glucose,  especial  interest  centres  round  this  body. 

In  the  alimentary  canal  the  higher  carbohydrates  are  trans- 
formed into  the  simpler  by  hydrolysing  enzymes.  The  simpler 
carbohydrates  are  all  represented  empirically  by  the  formula  CHgO. 
The  simplest  is  CHoO,  formaldehyde,  probably  first  produced  in  the 
plant  from  CO^  and  H2O  by  the  influence  of  sunlight  in  the  presence 
of  chlorophyll.     Glucose  has  been  synthesized  from  formaldehyde. 

Glucose  is  readily  prepared  by  hydrolysing  lactose,  maltose, 
starch,  and  cellulose.  When  treated  with  HI  it  loses  all  its 
oxygen,  and  is  converted  into  CgH^gl,  a  derivative  of  hexane, 
CH3.CH2.CH2.CH2.CH2.CH3.  Five  of  its  six  atoms  of  O  occur 
in  the  alcoholic  (OH)  form  and  one  in  the  aldehydic.  Owing 
to  its  stability  it  is  assumed  that  each  of  the  hydroxyls  is  linked 
to  a  different  carbon  atom;  its  constitutional  formula  may  be 
written  CH2.OH.CHOH.CHOH.CHOH.CHOH.CHO.  Since  glucose 
is  much  less  active  than  its  hydroxy-aldehydic  character  indicates, 
and  by  reason  of  its  general  reactions,  it  has  been  assumed  (and  the 
assumption  has  met  with  the  highest  support)  that  four  of  its  six 
carbon  atoms  and  one  oxygen  atom  are  arranged  in  the  form  of  a 
pentagonal  ring,  and  that  when  by  hydrolysis  the  ring  is  broken,  it 
passes  into  the  aldehydic  form,  as  shown  on  p.  272. 

The  four  carbon  atoms  in  the  ring  and  also  that  immediately 
contiguous  to  the  ring  on  the  right  are  asymmetric,  so  that  the 
ring  form  may  be  written  in  either  of  two  ways,  constituting  an  a- 
and  a  /3-glucose.  This  conception  of  two  stereoisomeric  forms  of 
glucose  explains  better  than  any  other  the  gradual  change  (some- 
times increase,  but  generally  decrease)  in  optical  rotation  which 
occurs  in  the  freshly  dissolved  substance  until  a  constant  value  is 
obtained.  Glucose,  like  the  other  aldoses  and  ketoses,  is  a  reducing 
agent — i.e.,  it  greedily  absorbs  oxygen  from  alkahne  solutions  of 
metallic  oxides.     Alkaline  copper  solution  on  warming  becomes 


272 


PRACTICAL  SANITARY  SCIENCE 


red  cuprous  oxide,  and  ammoniacal  silver  solutions  form  a  metallic 
mirror. 

The  reaction  of  glucose  and  other  sugars  to  excess  of  phenyl- 
hydrazine  in  acid  solution  enabled  Fischer  to  demonstrate  the 

H  OH       H  OH 


CH.CH(0H).CH2(0H)  +  HgO; 


H  OH      H  OH 

\/         \/ 

c  c 


OH/^^ 


)CH.CH(0H).CH2(0H) 


^- 


-^ 


OH 


H  OH      H  OH 

c  c 


HO 


H 


/9' 


/CH.CH(OH)  .CHoCOH)  +  HoO. 


O 


HO 


chemistry  of  the  carbohydrates.  If  glucose  be  heated  with  excess 
of  phenylhydrazine  and  acetic  acid,  the  insoluble  osazone  separates 
after  some  time. 


SUGAR  273 

Glucose,  mannose,  and  fructose  give  the  same  phenylosazone. 
Glucose  is  transformed  into  the  hexahydric  alcohol  sorbitol  by 
reduction  with  sodium  amalgam;  in  like  manner  mannose  is  con- 
verted into  mannitol,  and  galactose  into  dulcitoL  Glucose  is 
oxidized  to  gluconic  acid  by  bromine ;  the  aldehyde  group  becomes 
carboxyl. 

Oxidation, by  nitric  acid  transforms  glucose  into  bibasic  saccharic 
acid. 

Glucose  is  rapidly  oxidized  in  the  animal  body  under  normal 
conditions  to  COg  and  HgO ;  but  when  combined  with  such  bodies  as 
chloral  and  camphor,  the  aldehyde  end  of  the  glucose  molecule 
escapes,  and  oxidation  takes  place  at  the  other  extremity,  producing 
glucuronic  acid,  which  is  excreted  in  the  urine. 

The  power  of  removing  toxic  substances  from  circulation  in 
combination  with  glucose  appears  to  be  common  to  both  the  animal 
and  vegetable  kingdoms.  The  salts  of  glucuronic  acid  in  animals 
are  analogous  to  the  glucosides  in  vegetables. 

Disaccharides  consist  of  two  six-carbon  atom  groups  joined  by 
an  oxygen  atom,  and  are  consequently  analogous  to  the  simple 
glucosides.  On  hydrolysis  they  split  into  their  constituent  hexoses, 
which  may  be  either  aldoses  or  ketoses.  One  hexose  reduces  cupric 
salts,  forms  an  osazonC;  and  displays  mutarotation  like  glucose ;  the 
other  fails  in  all  these  respects.  Maltose  and  lactose  belong  to  the 
first  class. 

Rubner's  isodynamic  law — viz.,  '  in  dietaries,  fats  and  carbo- 
hydrates are  mutually  replaceable  in  definite  proportions,  the  sole 
limitation  being  that  imposed  by  the  digestive  organs  '• — is,  in  the 
light  of  recent  work,  only  partially  true.  This  method  of  assessing 
the  value  of  a  dietary  on  its  caloric  value,  whilst  of  admitted  use,  is 
misleading.  It  takes  no  account  of  the  chemical  form  of  foodstuffs. 
It  is  now  certain  that  in  man  at  least  there  must  be  a  constant 
supply  of  carbohydrate  circulating  in  the  body  fluids.  Even  in 
advanced  starvation  the  glucose  content  of  the  blood  varies  but 
little  from  that  of  the  normal.  If  fat  be  largely  substituted  for 
carbohydrate,  the  output  of  N  rises,  and  this  rise  of  N  is  due  to  the 
demand  of  the  organism  for  sugar  which  is  extracted  from  amino- 
acids  —  in  a  word,  undue  katabolism  takes  place  in  the  most 
important  tissue  constituents.     This  protein  breakdown  cannot  be 


274  PRACTICAL  SANITARY  SCIENCE 

inhibited  by  the  administration  of  fat.  Again,  of  the  two  stereo- 
isomeric  forms  of  glucose,  one  is  preferentially  metabolized  by  the 
animal  organism.  It  may  be  fairly  stated  that  of  isomeric  synthetic 
foodstufifs  that  form  alone  is  assimilated  and  oxidized  that  occurs  in 
nature.     A  limit  is  thus  set  to  the  synthesis  of  foods. 

Manufacture  of  Canc-Sugar. — The  juice  of  the  cane  is  extracted 
by  the  rollers  of  the  crushing-mills,  and  is  freed  from  proteins, 
acids,  etc.,  by  '  defecation  ' — coagulation  of  albumins,  etc.,  and 
neutralization  with  milk  of  lime.  When  the  impurities  are  removed 
as  a  scum,  the  juice  is  subjected  to  evaporation  and  crystallization. 
The  raw  sugar  is  thus  separated  from  the  mother-liquor,  or  molasses. 

But  sugar  is  prepared  by  digesting  sliced  beets  with  warni  water, 
and  then  clarifying  as  above. 

Sugar  is  refined  by  clarifying  it  with  various  reagents — lime,  clay, 
acid  phosphate  of  calcium,  blood,  etc.  The  syrup  from  wliich  the 
purified  sugar  is  crystallized  is  sold  as  '  golden  syrup.' 

Sugar  is  met  with  in  all  conditions  of  purity : 

Raw  sugars  (brown  sugar,  etc.)  contain  from  0-5  to  5  per  cent, 
of  moisture;  refined  sugars  below  0-5  per  cent. 

The  ash  consists  of  lime,  oxides  of  K  and  Na,  alumina,  silica, 
and  runs  from  0-05  to  2  per  cent.  Sometimes  brown  sugars  contain 
sand. 

Aniline  dyes  are  employed  to  colour  sugars.  Such  samples  will 
turn  pink  on  addition  of  HCl  and  a  little  heat. 

The  natural  colour  of  sugar  is  not  extracted  with  alcohol;  if 
the  dyed  sample  be  extracted  with  this  reagent  in  the  absolute 
form,  and  a  little  wool  previously  mordanted  with  aluminium 
acetate  placed  in  the  solution,  the  wool  will  be  coloured  yellow. 
Further,  on  examination  of  the  crystals  with  a  microscope,  the  dye 
will  be  found  unequalljr  distributed. 

Beet-sugar  is  bleached  with  SO.,,  or  bone  black,  and  afterwards 
dyed  with  ultramarine. 

Cane-sugar  (sucrose)  is  dextrarotatory,  but  invert-sugar  (the 
product  of  hydrolysis)  is  laevorotatory  (fructose  is  more  Isvorota- 
tory  than  dextrose  is  dextrorotatory). 

Maltose  is  produced  by  the  action  of  diastase  on  starch.  It 
crystallizes  in  small  needles,  is  dextrorotatory,  and  displays  muta- 
rotation.     It  reduces  Fehling's  solution,  forms  a  phenylosazone. 


SUGAR  275 

and  reacts  in  other  ways  like  glucose.  When  hydrolysed  by  acids, 
it  forms  two  molecules  of  glucose;  maltose  is  fermented  only  by 
maltase.  The  enzymes  diastase,  invertase,  lactase,  and  emulsin 
fail  to  affect  it.  It  has  been  therefore  considered  as  a  glucose-a- 
glucoside,  since  a-glucosides  only  are  hydrolysed  by  matase. 

The  sugars  are  estimated  by  Fehling's  solution,  or  the  Pavy 
modification,  or  by  the  polarimeter.  Each  polarimeter  works  on 
its  own  '  normal  weight  of  sugar  ' — the  amount  of  sucrose  dissolved 
in  100  c.c.  of  water,  which  produces  a  deviation  of  100°  on  the 
sugar  scale,  or  66-5  angular  degrees.  The  Laurent  instrument 
takes  16-19  grammes,  the  Soleil  and  Schmidt  instruments 
26-05  grammes. 

Fehling's  solution  may  be  used  volumetrically,  as  already 
described,  or  gravimetrically,  in  which  case  to  the  boiling  Fehling 
is  added  a  measured  quantity  of  sugar  solution  insufficient  to  reduce 
all  the  copper;  the  CU2O  precipitate  is  washed,  dried,  and  weighed, 
or  reduced  to  metallic  copper  and  weighed. 

The  amount  of  cane-sugar  in  a  sample  may  be  determined  by 
transforming  it  to  grape-sugar,  and  estimating  the  amount  of  the 
latter  by  Fehling's  method.  The  inversion  is  performed  by  heating 
a  quantity  of  the  sugar  with  about  a  tenth  of  its  bulk  of  strong 
hydrochloric  acid  for  ten  to  fifteen  minutes  on  a  water-bath. 
The  inverted  fluid  before  titration  is  neutralized  with  sodium 
carbonate. 

The  other  items  of  the  analysis  are  carried  out  by  the  usual 
methods. 

Tea. — Tea  consists  of  the  dried  leaves  of  several  varieties  of 
Camella  thea.  The  leaves  are  prepared  for  microscopical  examina- 
tion by  soaking  in  water  until  they  assume  their  original  shape,  when 
they  are  carefully  dried  between  layers  of  blotting-paper  and 
mounted  on  large  microscopic  slides  in  Farrant's  solution.  The  leaf 
is  elliptical,  and  possesses  an  emarginate  apex.  The  ribs  form  a 
looped  network,  arranged  symmetrically  on  either  side  of  the  mid- 
rib, and  approaching,  but  not  quite  reaching,  the  edge  of  the  leaf, 
thereby  leaving  a  clear  marginal  space.  The  margin  is  serrated 
from  a  point  near  to  the  apex  to  another  point  some  little  distance 
from  its  attachment  to  the  stalk;  the  point  of  each  serration  is 
surmounted  by  a  small  spine. 


276 


PRACTICAL  SAXITARY  SCIENCE 


When  a  leaf   is  immersed  in  a  warm  20  per  cent,  solution  of 
NaOH,  mounted  on  a  slide,  and  the  cover-slip  pressed  down,  long 


-ri^^. 


Fig.  69. — Cuticle  of  Tea-Leaf,     x  200. 


Fig.  70. — Idioblasts  in  Section  of 
Tea-Leaf.      X  160. 


Fig.  71. — Tea-Leaf. 


tenacious,  branched  cells,  temied  idioblasts,  are  to  be  seen.     These 

cells  do  not  occur  in  anj^  other  leaves  likely  to  be  mistaken  for  tea. 

Black  and  green  teas  differ  only  in  their  mode  of  preparation. 


TEA 


277 


Composition  of  an  Averag-e  Sample  of  Black  Tea : 


Water          

. .         8-2 

Thein 

. .       3-2 

Tannic  acid 

. .     16-4 

Pectin,  cellulose,  chlorophyll     . . 

. .     40-6 

Proteins 

. .     i8-o 

Alcoholic  extract  .  . 

•  •       7-3 

Ash             

.  .       6-3 

Of  these  constituents,  the  most  important  are  the  alkaloid  thein 
and  tannic  acid,  for  these,  with  0-5  per  cent,  of  volatile  oil,  produce 
the  characteristic  effects  of  tea. 

Indian  and  Ceylon  teas  are  richer  in  all  three  constituents  (thein, 
tannin,  volatile  oil)  than  China  teas ;  and  green  tea  is  richer  in  tannic 
acid  than  black;  but  the  amount  of  thein  is  about  the  same  in  both. 

If  tea  be  infused  for  five  minutes  in  the  usual  manner,  about 
one-fourth  of  the  weight  of  the  leaf  goes  into  solution.  The  thein 
is  so  soluble  that  it  passes  into  solution  almost  immediately,  but  the 
tannic  acid  requires  some  time  to  dissolve.  There  is  less  tannic 
acid  after  three  minutes'  solution  than  after  five,  and  less  after 
five  than  after  ten;  after  a  longer  interval  there  is  not  very  much 
change,  as  practically  all  the  soluble  materials  have  been  extracted 
in  ten  minutes;  therefore  the  less  tannic  acid  desired,  the  shorter 
should  be  the  time  of  infusion.  The  method  of  infusion  is,  from  a 
health  point  of  view,  more  important  than  the  character  of  leaf 
used.  First,  the  water  should  be  of  medium  hardness,  well  aerated, 
and  just  brought  to  the  boiling-point,  when  tea  is  infused.  If  the 
water  be  too  hard,  the  lime  and  other  salts  present  interfere  with 
the  extraction  of  some  of  the  constituents  of  the  leaf;  if,  on  the 
other  hand,  it  be  too  soft,  an  unpleasant,  bitter  material  is  ex- 
tracted. Infusion  should  last  for  about  three  minutes,  as  not  only 
does  prolonged  infusion  extract  too  much  tannic  acid,  but  it  also 
dissipates  the  volatile  oil  to  which  the  fragrance  of  tea  is  largely 
due.  A  further  point  of  import  is  that  too  much  leaf  should  not 
be  infused;  considerably  less  than  the  proverbial  teaspoonful  per 
head,  when  properly  infused,  is  sufficient  to  produce  the  most 
fragrant  and  pleasant  beverage.  The  addition  of  milk  to  tea, 
through  the  proteins  that  it  contains,  tends  to  precipitate  some  of 
the  tannic  acid.     Sugar  adds  considerably  to  its  nutritive  value. 


'.jS 


PRACTICAL  SAXITARY  SCIEXCE 


7'he  average  proportions  of  the  three  active  ingredients  in  ordinary 
teas  in  use  at  the  present  day  are  roughly  as  follows : 


The  in 

Tannin 
Volatile  oii  . 


2  to    4  per  cent. 
10  to  12         ,, 
0-5 


Adulteration. — ^Admixture  with  foreign  leaves,  such  as  elder-leaf, 
sloe-leaf,  and  the  leaf  of  the  willow,  has  been  effected.  A  low- 
power  microscope  readily  detects  any  of  these  (the  leaves  most 
commonlj-  employed)  from  the  tea-leaf,  as  none  of  them  possess  an 


Fi-G.  72. — Elder-Leaf.      Fig.  73. — Willow-Leaf.      Fig.  74. — Sloe-Leaf. 

emarginate  apex,  nor  do  their  systems  of  venation  leave  a  clear 
space  within  the  margin.  The  employment  of  infused  leaves  has 
been  practised,  and  it  may  be  sometimes  difficult  to  distinguish 
certain  prepared  leaves  from  the  genuine  leaf.  Various  chemicals 
have  been  used  to  colour  and  '  face  '  previousl}^  infused  leaves, 
such  as  turmeric,  sulphate  of  lime,  Prussian  blue,  and  black-lead. 
Old  leaves  have  been  worked  up  with  sand  and  gum,  and  re-rolled. 
It  may  be  quite  impossible  to  detect  small  quantities  of  such  leaves 
in  adulterated  samples,  since  genuine  teas  vary  much  in  the  rela- 
tive amounts  of  their  constituents.  The  ash  of  tea  should  fall 
between  47  and  6-2  per  cent.,  and  the  ash  soluble  in  water  should 
not  fall  below  30  per  cent,  of  the  total  ash.     Reference  to  these 


TEA  279 

figures  will  often  assist  in  arriving  at  a  conclusion  as  to  whether 
or  not  used  leaves  have  been  added.  In  faced  teas  the  ash  is  some- 
times 10  per  cent.,  whilst  in  exhausted  teas  it  is  rarely  more  than 
0-8  per  cent.  The  weight  of  the  ash  is  determined  by  carefully 
incinerating  a  convenient  quantity  of  tea — say  5  grammes — in  a 
platinum  dish,  and  weighing  the  greenish-grey  mineral  residue. 
This  is  the  total  ash.  The  contents  of  the  dish  are  next  treated 
with  boiling  water,  and  thrown  on  a  Swedish  filter-paper.  The 
insoluble  portion  is  thoroughly  washed  on  the  filter  with  water, 


'?r^ 


Fig.  75. — Cuticle  of  Tobacco-Leaf,     x  200. 

reignited,    and  weighed.      The   difference   between   this   and   the 
previous  weight  represents  the  soluble  ash. 

Estimation  of  Thein. — ^This  estimation  is  also  of  value  where  the 
presence  of  exhausted  leaves  is  suspected.  Extract  5  grammes  of 
finely  powdered  tea  with  300  c.c.  of  boiling  water,  in  a  flask  fitted 
to  a  reflex  condenser,  for  two  hours.  Repeat  the  extraction  a 
second  and  third  time,  allowing  two  hours  in  each  case.  Collect 
the  three  extracts  in  a  beaker;  add  neutral  lead  acetate,  and  boil 
for  ten  minutes.  Filter.  Free  the  filtrate  from  lead  by  passing 
through  it  HgS.  Evaporate  to  dryness  on  a  water-bath  with  some 
freshly  ignited  magnesia  and  clean  sand,   and  when  thoroughly 


28o  PRACTICAL  SANITARY  SCIENCE 

dry,  powder,  and  carefully  extract  with  chlorofonii  in  a  Soxhlet 
apparatus.  Evaporate  the  chloroform  extract,  and  boil  the  residue 
with  water.  Filter.  Evaporate  the  filtrate  to  dryness;  continue 
the  dr\nng  at  a  temperature  under  ioo°  C.  Weigh,  to  obtain  the 
amount  of  thein  in  5  grammes  of  tea.  Thein  under  the  microscope 
appears  as  long,  white,  silky  needles.  If  the  preliminary  extrac- 
tions are  not  thoroughly  performed,  some  of  the  thein  will  remain 
in  the  tissues  of  the  leaf. 

A  short  and  rapid  method  of  detecting  thein  in  tea-leaves  is  the 
following:  Take  two  watch-glasses  of  the  same  size,  and  place  in 
one  a  small  quantity  of  tea,  and  cover  with  the  other.  Mount  the 
pair  on  a  wire  gauze  over  a  small  Bunsen  flame.  In  five  minutes 
the  upper  glass  will  exhibit  numerous  drops  of  moisture;  in  ten 
minutes  some  fine  needles  of  thein  will  be  seen;  and  in  fifteen 
minutes  a  thick  crop  of  fulh^  formed  needles  will  have  condensed 
on  the  watch-glass.  Exhausted  leaves  produce  no  such  cr^-stals. 
If  the  watch-glass  be  floated  on  cold  water,  crystallization  is  has- 
tened. 

Catechu  is  added  to  tea  to  produce  a  semblance  of  richness  to 
the  infusion.  When  present  in  quantity,  it  may  be  detected  by 
precipitating  an  infusion  of  tea  with  neutral  lead  acetate  and 
filtering.  Five  c.c.  of  the  filtrate,  when  mixed  with  2  drops  of 
dilute  ferric  chloride  solution,  assume  a  green  colour,  which  ulti- 
mately settles  as  a  darker  precipitate. 

Estimation  of  Tannin :  Proctor  s  Modification  of  LowenthaV s 
Method. — Ascertain  how  much  permanganate  of  potassium  is 
reduced  by  tannic  acid,  and  other  readily  oxidizable  substances 
in  the  infusion.  Precipitate  the  tannin  by  gelatin,  and  once  more 
determine  the  amount  of  permanganate  reduced.  The  difference 
represents  the  quantit}^  of  permanganate  decomposed  b}^  tannin. 

Boil  5  grammes  powdered  tea  in  400  c.c.  water;  cool,  and  make 
up  to  500  c.c.  To  10  c.c.  filtered,  if  necessary,  add  25  c.c.  indigo 
carmine  solution  (6  grammes  indigo  and  50  c.c.  concentrated  H2SO4 
per  litre),  and  about  750  c.c.  water.  Run  in  from  a  burette  potas- 
sium permanganate  solution  (about  1-33  grammes  per  litre)  a  little 
at  a  time,  stirring  the  while  till  the  colour  becomes  light  green,  then 
drop  bv  drop  till  the  colour  changes  to  bright  3-ellow  or  faint  pink 
at  the  rim.     Let  the  number  of  c.c.  permanganate  used  =  a. 


TEA 


Mix  100  c.c.  of  the  clear  infusion  with  50  c.c.  gelatin  solution 
(25  grammes  gelatin  soaked  for  an  hour  in  saturated  NaCl  solution, 
heated  till  dissolved,,  cooled,  and  made  up  to  a  litre),  and  100  c.c. 
of  a  solution  consisting  of  975  c.c.  saturated  NaCl,  and  25  c.c.  con- 
centrated H2SO4;  add  10  grammes  powdered  kaolin,  and  shake 
well  in  a  stoppered  flask.  When  settled,  decant  the  clear  fluid  on 
a  filter,  and  afterwards  bring  the  precipitate  on  the  filter.  To 
25  c.c.  of  the  filtrate,  corresponding  to  10  c.c.  of  the  original  in- 
fusion, add  25  c.c.  indigo  carmine  solution  (6  grammes  indigo 
carmine  and  50  c.c.  concentrated  H2SO4  per  litre)  and  750  c.c.  water, 
and  titrate  with  permanganate  as  above. 

Let  the  number  of  c.c.  permanganate  used  =6. 

Now  a  =  permanganate  required  to  oxidize  all  oxidizable  sub- 
stances present,  and  &=  quantity  of  permanganate  required  to 
oxidize  substances  other  than  tannin.  Therefore  the  difference 
«—&=  permanganate  required  to  oxidize  the  tannin.  Titrate  the 
number  of  c.c.  permanganate  represented  by  a  — &  against  ^^  oxalic 
acid.  Assuming  that  0-063  gramme  oxalic  acid=  0-04157  gramme 
tannin  (gallotannic  acid),  the  amount  of  tannin  is  readily  calcu- 
lated. 

Coifee.— Coffee  is  derived  from  Caffea  arahica.  The  bean  is 
enclosed  in  an  outer  layer  of  fruit  like  the  stone  in  a  cherry,  and 
consists  of  two  symmetrical  halves  faced  together,  and  covered  by 
a  husk.  The  external  pulp  is  removed  by  fermentation,  and  the 
beans  are  dried  in  the  air;  later,  the  husk  is  separated  by  rolling. 
Many  varieties  of  bean  are  to  be  found,  the  finest  of  which  is 
Mocha.  The  beans  must  be  roasted  in  order  to  prepare  the 
beverage.  The  composition  of  raw  and  roasted  Mocha  coffee- 
beans  is  as  follows: 

Caffein 

Caffeic  acids 

Sugar 

Alcoholic  extract   . . 

Fats . . 

Legumin,  dextrin,  cellulose 

Moisture 

Ash 

The  roasting  of  coffee  dissipates  a  small  quantity  of  caffein  and 
about  10  per  cent,  of  fat,  and  produces  an  oil — caffeol — to  which 


Raw. 

Roasted. 

I -08      . 

0-82 

8-46      . 

-        474 

9-55     • 

•       0-43 

6-go     . 

■     14-14 

12-60     . 

•     13-59 

48-69     . 

.     60-09 

8-98     . 

.       0-63 

374     ■ 

•       4-56 

282  PRACTICAL  SAXITARY  SCIEXCE 

the  aroma  of  roasted  coffee  is  due.     It  precipitates  the  albumins 
and  separates  some  carbon. 

Caffein  is  almost  identical  chemically  with  thcin,  but  whilst  thein 
is  combined  with  tannin  in  the  form  of  a  tannate,  caffein  is  com- 
bined with  an  acid  allied  to  tannin  (caffetanic  acid),  which  is  not 
particularly  astringent,  does  not  coagulate  gelatin,  does  not  pre- 
cipitate alkaloids  (quinine,  etc.),  and  gives  a  light-green  coloration 


Fig.  76. — Coffee  Berrv.      x  30. 

with  FcaClg  instead  of  the  thick  black  liquid  produced  by  thein  and 
tannin. 

Thein  tannate  is  not  very  soluble  in  cold  water,  but  easily  soluble 
in  hot.  The  caffein  compound  is  readily  soluble  in  cold  w-ater. 
When  coffee  infusion  is  saturated  with  (NH4)2S04  a  precipitate  is 
obtained  which  contains  a  small  proportion  of  the  total  caffein  in 
the  free  state;  in  tea  infusion  similarly  treated  nearly  all  the  thein 
is  precipitated. 

The  tea  compound  is  precipitated  with  weak  acids,  and  presum- 
ably by  the  acid  of  the  gastric  juice,  and  is  accordingly  not  absorbed 
till  it  reaches  the  alkahne  small  intestine.     The  coffee  compound  is 


COFFEE  283 

soluble  in  both  acids  and  alkalies,  and  is  absorbed  from  both 
stomach  and  small  intestine. 

The  food  value  of  coffee  is  very  small.  It  diminishes  nervous 
fatigue  somewhat,  and  thus  assists  muscular  contraction.  It  is  in 
some  degree  an  antidote  to  alcohol. 

Adulteration  of  Coffee. — The  principal  foreign  substance  found  in 
coffee  is  chicory,  a  preparation  of  the  root  of  the  wild  endive. 
Although  the  sale  of  chicory  is  allowed,  and  its  admixture  with 
coffee  is  very  general,  it  is  fraudulent  to  add  it  to  samples  sold  as 


Fig.  77. — Ground  Coffee,  showing  Cells  of  Testa,     x  100. 

pure  coffee.  The  quantity  of  chicory  added  to  coffee  varies  very 
much,  reaching  sometimes  90  per  cent,  of  the  whole.  It  imparts  a 
slightly  bitter  flavour  to  coffee,  but  is  used  principally  to  blacken 
and  thicken  it.  Chicory  is  easily  distinguished  by  the  following 
characters:    (i)    Its   odour   is    very    different    to   that    of    coffee. 

(2)  Roasted  chicory  sinks  in  water  rapidly,  whilst  roasted  coffee 
floats  for  some  time,  and  sinks  slowly,  owing  to  the  oil  in  the  coffee 
preventing  the  particles  being  readily  moistened.  Moreover,  the 
sediment  of  the  coffee  remains  hard,  whilst  that  of  chicory  is  soft. 

(3)  The  specific  gravity  of  a  10  per  cent,  infusion  of  dried  chicory 
in  water,  raised  to  the  boiling-point,  maintained  thereat  for  thirty 


284 


PRACTICAL  SAX  IT  A  RY  SCIENCE 


seconds  and  filtered,  is  rarely  below  i.oiS,  and  averages  about 
1,022.  The  specific  gravity  of  a  coffee  infusion  prepared  in  the 
same  manner  is  never  higher  than  i,oio,  and  averages  i,oo8. 
Other  and  rarer  adulterants,  such  as  ground  carrots,  turnips,  etc., 
will  give  infusions  of  specific  gravities  of  1,015  ^^"d  over.  (4)  Micro- 
scopic examination  of  the  powder  will  demonstrate  the  character- 
istic dotted  and  lacteal  ducts  of  chicory,  whereas  in  coffee  portions 
of  the  membrane  or  testa  hning  the  berry,  and  containing  the  char- 
acteristic spindle  cells,  will  appear,  as  also  endosperm  cells.  (5)  All 
foreign  bodies  added  to  coffee  are  devoid  of  caffein.  (6)  If  to  a 
5  per  cent,  infusion  of  pure  coffee  is  added  a  shght  excess  of  basic 
lead  acetate,  a  precipitate  falls,  leaving  a  colourless  supernatant 
fluid:  the  corresponding  supernatant  fluid  in  chicory  is  coloured. 


Fig.  7S. — Lacteal  Vessels 
OF  Chicory,     x  100. 


Fig.  79. — Dotted  Vessels 
OF  Chicory,      x  too. 


When  acorns,  potatoes,  sago,  etc.,  are  mixed  with  coffee,  micro- 
scopic examination  will  detect  their  starch  granules.  Infusions  of 
coffee  and  pure  chicory  are  not  blued  by  iodine.  Caramel  may  be 
detected  by  its  shining  particles  when  viewed  with  a  hand  lens,  as 
they  stand  out  in  contrast  with  the  dull  particles  of  coffee;  also 
by  its  ready  solubility  in  water. 

Various  artificial  coffee-beans  containing  little  or  no  real  coffee 
have  been  found  at  times  upon  the  market.  Coffee  extracts  are 
deficient  in  caffein. 

Estimation  of  Caffein. — The  method  described  for  the  estimation 
of  thein  may  be  used.  An  alternative  method  is  the  following: 
Moisten  10  grammes  finely  powdered  coffee  with  2-5  to  3  c.c.  water; 
stand  for  half  an  hour.  Extract  with  CHCI3  for  three  hours  in  a 
Soxhlet.     Evaporate  the  extract.     Treat  the  residue  of  fat  and 


COCOA 


28  = 


caffein  with  hot  water;  filter  through  a  cotton  plug,  and  wash  with 
hot  water.  Make  up  the  filtrate  and  washings  to  50  c.c.  Pipette 
off  40  C.C.,  and  extract  four  times  in  a  separator  funnel  with  CHCI3. 
Evaporate;  dry  the  caffein  at  100°,  and  weigh.  Calculate  the 
percentage. 

Coeoa. — Cocoa  is  prepared  from  the  seeds  of  a  cucumber-like 
fruit — Theobroma  cacao.  The  seeds  are  separated  from  the  fruit, 
heaped  together  for  some  days,  and  allowed  to  ferment,  which 
modifies  their  bitterness  and  darkens  their  colour.  They  are  next 
roasted,  when  the  symmetrical  halves  of  the  seed  separate  as  cocoa- 
nibs  on  being  submitted  to  pressure  in  a  machine.  The  nibs  may 
be  sold  in  this  form,  or  they  may  be  ground  between  hot  rollers. 
In  the  latter  case  the  fat  is  melted,  and  the  products  of  grinding 
are  consequently  reduced  to  a  fluid.  A  considerable  portion  of  the 
fat  is  removed  by  pressure,  and  the  remainder,  having  been  run  into 
moulds,  and  thus  converted  into  solid  slabs,  is  once  more  ground 
and  sold  as  a  powder.  Strictly  speaking,  cocoa  is  not  soluble  in 
water;  the  Dutch  manufacturers  add  alkalies  to  it,  which  saponify 
the  fat  and  somewhat  soften  the  fibres  of  the  cocoa. 

Composition  of  Cocoa  as  Raw  Nibs: 


Fat            

.  .        50-44 

Starch 

4-26 

Proteins    . . 

.  .        13-20 

Various  astringents 

6-71 

Gum  and  cellulose 

•  •      8-57 

Other  non-nitrogenous  bodies  . 

. .       5-8o 

Colouring  matter 

2-20 

Alkaloid   . . 

0-84 

Water 

•  •       5-23 

Ash           

_  1 • 

•  -      2-75 

The  chief  alkaloid  of  cocoa  is  theobromine  (dimethyl-xanthin), 
a  body  closely  related  to  caffein.  In  the  commercial  powder  the 
50  per  cent,  of  fat  is  reduced  to  30,  or  under. 

Adulterants. — Foreign  starches,  which  can  be  more  or  less  easily 
detected  by  the  microscope.  Alkahes  are  frequently  added  in 
considerable  quantities  for  the  purpose  of  increasing  the  solubility 
of  the  cocoa.  A  determination  of  the  ash,  which  in  unadulterated 
varieties  rarely  exceeds  4  per  cent.,  will  assist  in  detecting  such 
additions. 


286  PRACTICAL  SAXITARY  SCIENCE 

Chocolate  is  ground  cocoa  irom  which  the  fat  has,  or  has  not, 
been  removed.  Sugar,  starch,  and  various  flavouring  materials 
are  added,  and  the  whole  melted  and  thrown  into  moulds,  or  pre- 
pared for  distribution  in  other  ways. 

Theobromine  may  be  estimated  thus:  Remove  the  fat  and 
caffein  bv  petroleum  spirit,  and  dry  the  extract  on  the  water-bath. 
Boil  this  extract  in  water  for  a  considerable  time.  Next  extract 
the  residue  not  affected  by  petroleum  with  chloroform  for  several 
hours  in  a  Soxhlet  apparatus.  Drive  off  the  chloroform  on  a  water- 
bath,  and  boil  the  extract  several  times  w'ith  water.  Mix  the  two 
extracts  in  water,  and  evaporate  to  dryness  in  a  platinum  dish. 
Weigh  the  residue  as  theobromine. 


CHAPTER  XII 

DISINFECTANTS 

Until  comparatively  recent  years  no  very  marked  distinction 
was  made  between  disinfectants,  antiseptics,  and  deodorants;  and 
this  statement  applies  not  only  to  the  lay  public,  but  also  to  sani- 
tarians. The  explanation  is  that,  through  lack  of  definite  and 
exact  experimental  knowledge  concerning  the  physical  and  chemical 
nature  of  the  work  to  be  done  in  disinfection,  and  of  the  agents 
employed  therein,  quite  erroneous  views  were  held  upon  both. 
Prior  to  the  days  of  origin  of  bacteriology,  a  disinfectant  included, 
besides  certain  physical  conditions,  any  body  capable  of  destroying 
infective  or  putrefactive  matter,  especially  the  noxious  odours  con- 
nected with  putrefaction.  The  disposal  of  dead  and  putrefying 
animal  and  vegetable  substances,  more  especially  the  bodies  of  dead 
animals  and  the  human  subject,  has  been  a  matter  of  special  in- 
terest to  man  from  his  earliest  days,  as  witnessed  by  the  manner 
in  which  it  is  interwoven  with  the  most  sacred  religious  rites  of  the 
oldest  nations.  That  important  evils  in  the  form  of  disease  arose 
from  lack  of  proper  attention  to  such  disposal  was  understood,  but 
of  the  mode  of  production  of  such  conditions  nothing  was  truly 
known  until  bacteriology  demonstrated  the  existence  of  putrefac- 
tive and  pathogenic  micro-organisms. 

A  disinfectant  is  a  germicide  or  destroyer  of  germs.  An  anti- 
septic is  a  body  that  exerts  an  antagonistic  or  inhibitory  influence 
on  germs,  and  is  not  necessarily  a  disinfectant.  A  deodorant  may 
possess  neither  antiseptic  nor  disinfectant  properties. 

Koch  showed  in  1881  how  bacteria  and  their  spores  can  be  em- 
ployed in  the  scientific  study  of  disinfection.  Later  Kronig  and 
Paul  pointed  out  that  the  power  of  a  disinfectant  solution  depends 
on  certain  properties  inherent  in  the  salts  in  solution,  and  the  nature 

287 


288  PRACTICAL  SANITARY  SCIENCE 

of  the  solvent  employed.  Still  later  Bechold  and  Ehrlich  demon- 
strated certain  relations  which  exist  between  chemical  constitution 
and  disinfectant  action,  and  Bechold  published  his  views  on  the 
relations  which  exist  between  disinfection  and  the  chemistry  of  the 
colloids. 

We  have  known  for  some  years  that  certain  relations  exist 
between  the  constitution  of  chemical  substances  and  their  physio- 
logical action.  Antip3Tin,  for  example,  owes  its  analgesic  proper- 
ties to  the  presence  of  the  organic  radical  methyl  (CH3).  The 
introduction  of  a  second  meth}'l  group  forms  a  new  body  pos- 
sessing the  same  pain-allaying  properties  in  a  greatly  increased 
degree. 

Desgrez  pointed  out  in  191 1  that  non-saturation  of  the  molecule 
increases  the  toxicity  of  the  nitriles,  and  in  a  proportion  greater  as 
the  saturation  is  less.  The  corresponding  amides  are  subject  to 
the  same  law.  The  germicidal  power  of  an  organic  compound  is 
directly  proportional  to  the  number  and  kind  of  certain  radicals 
(phenyl,  methyl,  naphthyl),  or,  under  certain  conditions,  of  halogens 
(CI,  Br,  I),  found  in  the  body.  The  germicidal  activities  of  such 
radicals  differ  widely  amongst  themselves — e.g.,  the  group  phenyl 
(CgHj)  is  about  five  times  more  energetic  against  certain  bacteria 
than  methyl  (CH3).  Again,  oxygen  combined  with  carbon  and 
hydrogen,  and  even  with  nitrogen,  increases  the  bactericidal  power 
of  the  compound.  Nitrogen  combined  with  one  or  two  atoms  of 
hydrogen  always  lowers  antiseptic  power.  The  substitution  in  an 
amide  group  of  an  antiseptic  group  (phenyl,  naphthj^l,  etc.)  im- 
mediateh^  raises  the  bactericidal  powers  of  the  compound.  By  the 
accumulation  of  phenjd  groups  large  increase  in  germicidal  powers 
has  been  conferred  on  several  compounds.  Bechold  and  Ehrlich 
found  that  the  introduction  of  sulphonic  groups,  on  the  other  hand, 
lowers  germicidal  power.  Scholler  and  Schrauth  have  shown  that 
the  introduction  of  halogens  (CI  and  I)  in  the  benzene  nucleus  of 
oxymercuriobenzoate  of  soda  notably  augments  the  disinfectant 
power  of  this  bod}-.  But  after  a  certain  amount  of  halogen  has 
been  incorporated,  further  additions  fail  to  raise  it.  Bechold  and 
Ehrlich,  working  with  a  phenyl  group,  introduced  successively  one  to 
five  atoms  of  bromine.  The  disinfectant  powers  of  these  com- 
pounds for  staphj'lococci  and  streptococci  increased  until  three 


DISINFECTANTS  289 

atoms  were  reached,  remained  constant  for  the  fourth,  and  dimin- 
ished with  the  addition  of  the  fifth.  For  B.  coli  they  found  that 
the  maximum  efficiency  was  reached  with  the  second  bromine 
atom. 

In  1910,  working  with  a  phenyl  group,  the  author  was  able  to 
raise  the  germicidal  efficiency  for  B.  typhosus  20  per  cent,  by  the 
incorporation  of  a  small  amount  of  chlorine,  and  60  per  cent,  by 
saturation. 

The  action  of  germicidal  agents  increases  with  duration  of  con- 
tact, and  also  with  increase  of  concentration.  Working  with 
anthrax  spores  and  carbolic  acid,  Koch  showed  that  in  order  to 
produce  sterility,  it  was  necessary  to  employ  a  i  per  cent,  solution 
of  the  disinfectant  for  seven  days,  a  4  per  cent,  solution  for  three 
days,  and  a  5  per  cent,  solution  for  two  days. 

In  1889  Fraenkel  and  Henle  drew  attention  to  the  fact  that  the 
higher  homologues  of  phenol  contained  in  the  creolins  of  those  days 
are  more  powerful  germicides,  and,  being  much  more  insoluble,  are 
less  toxic  than  phenol.  Fraenkel  and  Behring  at  this  time  tested 
various  disinfectants,  using  Koch's  silk  threads  impregnated  with 
anthrax  spores;  but  after  removing  the  threads  from  the  disinfect- 
ant fluids,  they  transferred  them  to  peptone  bouillon,  instead  of 
solid  media,  as  Koch  had  done. 

In  1897  Kronig  and  Paul  used,  instead  of  threads,  small  sterile 
Bohemian  garnets  of  uniform  size,  which  they  shook  in  the  emulsion 
of  anthrax  bacilli  or  spores,  staphylococci,  etc.  From  time  to  time 
a  definite  number  were  taken  out,  and  after  the  disinfectant  had 
been  removed  by  washing,  these  were  well  shaken  in  a  measured 
quantity  of  water  to  remove  the  spores;  a  fractional  amount  of 
the  washings  was  plated,  and  the  number  of  germinating  spores 
counted. 

In  1907  Madsen  and  Nyman  confirmed  Kronig  and  Paul's  work, 
and  also  the  conclusion  that  had  already  been  drawn  from  their 
figures  by  Ikeda — viz.,  that  the  disinfection  of  anthrax  spores  pro- 
ceeded after  the  manner  of  a  unimolecular  chemical  reaction,  in 
which  the  velocity  of  chemical  change  at  any  instant  is  propor- 
tional to  the  active  mass  of  reacting  substance  present  at  that 
instant.     If  for  concentration  (mass  of  reacting  substance)  there  be 

19 


2go  PRACTICAL  SAXITARY  SCIENCE 

substituted  nnmhcr  of  surviving  spores,  the  unimolecular  reaction 
equation —  \ 


becomes — 


d  t 


They  showed  that  the  disinfection  of  anthrax  spores  by  heat  con- 
formed to  the  same  equation. 

Reichert  in  1909  showed  that  heat-coagulated  serum  absorbed 
phenol  fromaqueous  solution  in  amount  directly  proportional  to 
concentration.  He  demonstrated  further  that  the  addition  of  a 
neutral  salt  like  sodium  chloride  increased  both  the  quantity  of 
phenol  absorbed  and  its  germicidal  power. 

Cooper,  in  1912,  proved  that  egg  albumin  and  gelatin  absorb 
phenol  and  metacresol  according  to  the  partition  law;  and  that 
when  a  certain  phenol  concentration  is  reached,  the  proteins  are 
precipitated,  whereby  they  take  on  a  greatly  increased  capacity 
for  absorbing  phenol.  The  precipitation  of  gelatin  by  phenol  is 
reversible,  and  that  of  egg  albumin  irreversible.  Certain  polypep- 
tides are  not  precipitated  by  strong  solutions  of  phenol.  Cresols 
precipitate  proteins  in  lower  concentrations  than  phenol.  The 
absorption  of  cresols  and  phenol  by  proteins  is  about  the  same. 
It  appears  that  the  inclusion  in  the  benzene  ring  of  the  radical 
methyl  (CHg)  increases  both  protein-precipitating  and  germicidal 
powers,  but  produces  no  change  in  the  initial  absorption  of  phenol 
by  protein;  hence  it  is  argued  that  selective  germicidal  action  is 
determined  by  the  phenol- concentration  at  which  particular  pro- 
teins are  precipitated,  and  that  the  disinfectant  action  of  phenol  is 
a  mechanism  similar  to  that  of  heat. 

Watery  solutions  of  antiseptics  and  disinfectants  are  more 
powerful  than  alcohohc,  ethereal,  and  other  solutions  in  which 
electrical  dissociation  is  feeble.  Koch  showed  that  anthrax  spores 
are  not  destroyed  by  5  per  cent,  phenol  in  oil  in  100  days,  nor  by 
the  same  percentage  in  alcohol  in  70  days,  whilst  5  per  cent,  con- 
centration in  water  kills  in  48  hours.  These  remarks  apply  to 
iodine,  thymol,  salicylic  acid,  and  other  bodies. 

Gaseous    disinfectants,    such    as    chlorine,    formaldehyde,    etc., 


DISINFECTANTS  291 

require  a  certain  amount  of  water,  or  humidity  of  atmosphere, 
for  the  development  of  their  activities.  This  is  in  accordance  with 
the  fundamental  principle  that  chemical  reactions  take  place  in 
solution.  Antiseptics  dissolved  in  anhydrous  alcohol  have  as  a 
rule  no  more  disinfectant  action  on  bacteria  than  that  due  to  the 
alcohol  dissolving  them,  which,  owing  to  its  dehydrating  proper- 
ties, possesses  a  germicidal  action  analogous  to  that  of  desiccation 
by  air.  It  has  been  shown  that  in  a  mixture  of  water  and  alcohol 
osmotic  currents  are  established  between  the  bacterial  cells  and 
the  menstruum.  Thus,  whilst  in  pure  alcohol  bacteria  contract, 
owing  to  dehydration,  in  a  mixture  of  alcohol  and  water  they  swell, 
thereby  offering  an  entrance  to  disinfectants. 

In  the  case  of  germicides  insoluble  or  but  slightly  soluble  in 
water,  as  salicylic  acid,  thymol,  etc.,  activity  may  be  secured  by 
associating  them  with  bodies  which  dissolve  them,  or  by  incor- 
porating them  in  certain  chemical  groups,  such  as  sulpho 
groups. 

The  metallic  ion  appears  to  be  the  true  agent  of  disinfection  in 
metallic  salts.  These  are  found  in  liquids  other  than  water  (alco- 
hol, ether,  etc.)  in  a  state  of  feeble  electric  dissociation;  whilst  in 
water  free  ionization  takes  place.  Hence  the  superiority  of  watery 
preparations  of  salts  as  disinfectants. 

Germicidal  power  is  accordingly  proportional  to  the  intensity  of 
ionization.  Such  an  assumption  permits  us  to  explain  a  number  of 
experimental  facts,  but  not  all.  It  enables  us  to  conceive  how  the 
action  of  a  disinfectant  solution  is  inhibited  by  the  addition  of  one 
or  more  extraneous  substances.  The  decrease  in  activity  of  a 
solution  of  perchloride  of  mercury  by  the  addition  of  sodium 
chloride  is  evidently  due  to  a  modification  of  dissociation.  A 
quantity  of  free  ions  is  employed  for  the  dissociation  of  the  sodium 
chloride,  and  consequently  a  less  number  of  mercury  ions  remains 
for  disinfection.  The  addition  of  acids  to  solutions  of  perchloride 
of  mercury  acts  in  the  same  manner. 

Again,  the  germicidal  powers  of  acids  do  not  depend  on  their 
chemical  energy,  but  on  the  degree  of  ionization  to  which  each  can 
be  individually  subjected.  Sulphuric  acid  can  displace  nitric  and 
hydrochloric  acids  by  reason  of  its  greater  chemical  energy;  but 
its  germicidal  activity  is  less  than  that  of  either  by  reason  of  its 


2  92  PRACTICAL  SANITARY  SCIENCE 

smaller  electro-chemical  dissociation,  wherein  fewer  ions  are 
liberated. 

Soda,  potash,  and  ammonia  are  germicidal  in  proportion  to  the 
concentration  of  the  OH  ions. 

Whilst  the  addition  of  certain  substances  hinders  the  action  of 
certain  disinfectants  by  modification  of  dissociation,  in  other  cases 
disinfectant  action  is  assisted  by  such  additions. 

Phenol  appears  to  act  in  disinfection  as  a  molecule  and  not  as  an 
ion;  phenylate  of  sodium,  which  is  readily  dissociated,  has  a  much 
less  germicidal  value  than  phenol. 

When  a  reaction  takes  place  in  a  heterogeneous  system,  certain 
changes  other  than  purely  chemical  occur.  Since  the  reacting 
bodies  are  not  unifomily  distributed,  one  is  compelled  to  travel  a 
certain  distance  to  come  into  contact  with  the  other;  diffusion  is 
therefore  a  preliminary  stage  of  the  reaction.  At  the  interfaces 
where  the  phases  are  in  contact,  there  is  an  accumulation  of  sur- 
face energy.  It  is  known  that  chemical  and  other  forms  of  change 
will  take  the  form  of  increase  of  concentration  at  a  surface  when 
the  potential  of  any  form  of  energy  at  that  surface  can  be  dimin- 
ished by  the  change.  This  concentration  of  bodies  on  the  surfaces 
of  contact  between  the  phases  of  heterogeneous  systems  where  such 
potential  is  diminished  is  known  as  '  adsorption.' 

If  at  this  stage  no  purely  chemical  reaction  occurs,  the  process 
stops ;  but  if  chemical  reaction  takes  place,  its  velocity  in  consonance 
with  the  law  of  mass  action  is  a  function  of  the  amount  adsorbed, 
and  is  much  greater  tlian  if  no  surface  condensation  had  taken 
place.  Adsorption  undoubtedly  plays  a  large  part  in  many  forms 
of  disinfection,  and  confers  upon  emulsions  as  contrasted  with  solu- 
tions considerable  advantages. 

Bacteria  present  an  enormous  surface  development.  If,  then, 
we  place  in  contact  an  emulsion  of  bacteria  and  a  solution  of  an 
antiseptic,  the  dissolved  substance  will  tend  to  concentrate  on  the 
surface  of  the  bacteria  more  or  less  strongly  according  to  their 
individual  nature. 

We  know  that  the  same  substance  is  a  better  germicide  in  aqueous 
solution  than  in  alcoholic;  we  also  know  that  adsorption  phenomena 
are  much  more  intense  in  aqueous  than  in  alcoholic  solution. 

Those  organic  radicals  which  possess  large  germicidal  powers. 


DISINFECTANTS  293 

such  as  phenyl,  naphthyl,  etc.,  influence  adsorption  ];irgely;  whilst 
other  radicals  which  are  destitute  of  germicidal  action,  such  as 
certain  sulpho-compounds,  are  but  little  adsorbed. 

But  ionization  and  adsorption  do  not  represent  the  wliolc  of  the 
phenomena  of  disinfection.  True  chemical  action  must  supple- 
ment these  preliminary  stages.  The  disinfectant  agent  is  not 
always  an  electrolyte.  Colloidal  metals  are  powerful  disinfectants. 
It  has  been  shown  that  a  i  in  80,000  solution  of  colloidal  silver 
sterilizes  pneumococci ;  and  about  equal  results  have  been  obtained 
for  this  reagent  with  B.  typhosus,  B.  coli,  and  dysentery  bacilli. 

Charrin  has  shown  that  of  two  lots  of  white  mice  inoculated  with 
pneumococci,  one,  treated  with  isotonic  colloidal  silver  of  small 
grains,  survived  infection;  whilst  the  other,  retained  as  a  control, 
died  in  thirty  hours.  Colloidal  silver,  according  to  this  observer, 
is  a  much  more  powerful  bactericide  than  salts  of  mercury,  and  is 
relatively  non-toxic.  Colloidal  mercury  has  been  shown  to  possess 
a  greater  germicidal  power  than  mercuric  chloride.  In  these  cases 
ionization  has  no  part. 

The  last  phase  in  the  disinfectant  action  of  certain  bodies  (CI, 
ozone,  etc.)  is  an  oxidation  of  living  protoplasm,  which,  in  some 
cases,  may  proceed  to  complete  combustion.  In  many  instances 
we  cannot  trace  the  action  further  than  a  precipitation  of  the  proto- 
plasm of  the  bacterial  cell. 

Traces  of  disinfectants  are  frequently  effective;  one  cannot  but 
connect  this  fact  with  another — viz.,  that  in  studying  adsorption 
curves  we  see  the  partition  between  adsorbent  and  solvent  take 
place  in  such  manner,  that  with  minimum  concentrations  the 
dissolved  substance  is  almost  completely  adsorbed.  As  Rochaix 
points  out,  this  explains  why  an  internal  antiseptic  acts  in  the 
tissues  despite  the  great  dilution  produced  by  their  fluids. 

Mere  inhibition  of  development  is  not  clearly  explicable  unless 
we  invoke  the  intervention  of  adsorption  phenomena. 

From  experimental  work  done,  it  is  now  justifiable  to  conclude 
that  in  the  process  of  disinfection  one  or  more  of  three  types  of 
activity  may  be  engaged:  (i)  Ionization  with  diffusion;  (2)  adsorp- 
tion; (3)  purely  chemical  action.  Further,  it  may  be  concluded 
that  the  last  type  is  usually  preceded  by  the  first  and  second  in 
case  the  disinfectant  is  an  electrolyte,  and  hy  the  second  when  the 


2  94  PRACTICAL  SANITARY  SCIENCE 

disinfectant  is  a  colloid,  and  that  the  preliminar}'  activities  are 
necessan'  to  the  final  action. 

In  organic  compounds  oxygen  causes  in  general  an  increase  in 
velocity  of  reaction,  and  tends  to  overcome  the  inertia  of  carbon. 
The  linkage  of  carbon  to  carbon  is  loosened  by  the  presence  of 
oxygen,  as  specially  seen  in  the  fact  that  all  carbon  chains  in  com- 
bustion in  oxygen  break  up  into  unlinked  carbon  dioxide.  Special 
explosive  linkages  are  C^^C,  0 — O,  and  O — CI. 

Hydrog'en  peroxide  as  an  oxidizing  agent  is  interesting  in  that 
its  mode  of  action  appears  to  be  very  similar  to  that  obtaining  in 
a  number  of  auto-oxidations  occurring  in  the  living  body.  Traube 
conceives  that  in  auto-oxidations  super-oxides  are  formed  b\'  the 
action  of  oxygen  carriers  on  molecular  oxygen,  and  that  ionization 
of  molecular  oxygen  does  not  necessarily  take  place  as  asserted  by 
Schonbein. 

Normally  saturated  fatty  acids  in  the  body  undergo  oxidation  in 
the  S  position:  butvric  acid  becomes  aceto-acetic.  H.,0o  produces 
the  same  change :  CH3.  CH,.  CH.,.  COOH  —>  CH3.  CO.  CH..  COOH. 
Glucose  is  oxidized  in  the  tissues  to  glycuronic  acid:  HoO.,  effects 
the  same  reaction — 

H„.  OH.  CHOH.  CHOH.  CHOH.  CHOH.  CHO 
— >COOH.  CHOH.  CHOH.  CHOH.  CHOH.  CHO. 

Indol  is  oxidized  to  indoxyl:  Yijd.,  brings  about  the  same  reac- 
tion— 

H 


^  /     \_COH 

"SCH    -- >    I        I    "^CH 


'N  \/     N 

H  H 

And  so  with  other  reactions. 

Such  similarity  of  action  is  not  only  interesting  from  an  academic 
point  of  view,  but  also  from  the  practical,  as  when  a  mild  antiseptic 
for  use  in  the  human  subject  is  to  be  selected. 

Hydrogen  peroxide  is  prepared  by  acting  on  a  peroxide  of  an 
alkaline  earth  by  an  acid,  and  other  means— 

BaO^  +  H^SO,  -  HoO,  +  BaS04. 


DISINFECTANTS  295 

Its  action  as  a  disinfectant  is  somewhat  slow.  It  is  said,  liow- 
ever,  not  to  have  the  same  tendency  to  oxidize  dead  organic  matter 
as  permanganates,  whilst  it  destroys  associated  bacteria.  It  has 
been  used  to  sterilize  water  and  milk. 

Estimation  of  H./)o. — This  body  is  sold  as  containing  5,  10,  or  20 
volumes  O  in  solution.  To  10  c.c.  peroxide  solution  under  test 
add  about  30  c.c.  H2SO4  (i  in  3)  in  a  beaker  (the  sulphuric  acid  must 
be  in  fairly  large  excess),  and  crystals  of  KI  in  excess,  and,  after 
standing  for  five  minutes,  titrate  the  liberated  I  with  y^  thiosul- 
phate  and  starch.  Before  testing,  solutions  of  peroxide  should  be 
diluted  to  the  strength  of  two  volumes  O — 

2HI  +  H,A=l2^  2H2O. 
I  c.c.  -^jj  thiosulphate  =  0-00085  gramme  H2O2, 
or  O" 0008  gramme  O. 

Ozone  is  formed  from  atmospheric  oxygen  in  a  variety  of  ways : 
When  phosphorus  is  left  in  contact  with  air,  it  is  slowly  oxidized 
and  ozone  formed.  Platinum  may  be  used  for  its  production. 
Permanganates  treated  with  concentrated  H2SO4  yield  ozone.  The 
most  common  and  most  inexpensive  method  of  procuring  it  is  by 
means  of  the  silent  electric  discharge.  Electrical  ozonizers  have 
been  erected  in  recent  years  for  the  sterilization  of  the  water  of  the 
Marne,  outside  Paris,  and  the  results  have  been  reported  as  good. 
Various  schemes  have  from  time  to  time  been  initiated  in  different 
countries  for  the  purification  of  the  air  of  towns,  public  buildings, 
and  private  dwellings,  by  ozone;  but  whether  advantageous  results 
have  accrued  from  any  of  these  undertakings  is  highly  doubtful. 

Free  chlorine  is  capable  of  killing  bacteria  by  combining  with 
and  coagulating  their  protoplasm.  Chlorine  destroys  the  offensive 
odour  of  HgS,  a  product  of  nitrogenous  putrefaction,  by  decom- 
posing it,  with  formation  of  HCl  and  S — H2S  +  Cl2=  2HCI  +  S. 
But  chlorine  acts  as  a  germicide  for  the  most  part,  by  combining 
with  the  hydrogen  of  water  and  liberating  nascent  oxygen — 

H20  +  Cl2  =  2HCl  +  0. 

The  liberated  O  is  the  disinfectant.  Light  increases  this  reaction. 
The  application  of  dry  chlorine  gas  in  disinfection  may  be  regarded 
as  useless. 


296  PRACTICAL  SAX  IT  A  RY  SCIEXCE 

In  the  so-called  chloride  of  lime  (;i  mixture  of  CaCl.,  and  Ca(OCl)o) 
and  other  hypochlorites,  such  as  chloros,  Hermite  solution,  etc., 
this  halogen  is  used  in  considerable  quantities.  Its  action  in  all 
these  cases  is  that  of  an  oxidizer. 

Chloride  of  lime,  or  bleaching  powder,  is  produced  by  passing 
chlorine  over  moist  lime,  and  is  preferred  to  the  soda  and  potash 
compounds  in  that  it  can  be  kept  as  a  dry  powder.  The  hypo- 
chlorite portion  is  strongly  alkaline,  and  in  the  presence  of  moisture 
reacts  with  the  CO.,  of  the  air  to  form  hypochlorous  acid  and 
calcium  carbonate — 

Ca(0Cl)2  +  H.O  +  CO.,  =  CaCOg  +  2HCIO. 

In  the  act  of  disinfection,  the  HCIO  sphts  into  HCl  and  nascent  O. 
One  part  of  fresh  bleaching  powder  to  ten  parts  of  water  has  been 
recommended  as  a  disinfectant  solution  for  general  work,  and  i  part 
to  100  of  water  as  a  solution  for  the  hands. 

When  solutions  of  chlorides  of  the  alkalies  or  alkaline  earths  are 
electrolyzed,  hypochlorous  acid  and  the  corresponding  hydrate  are 
formed— 

MgCl,  +  2H.,0  =  Mg(OH)o  +  2HOCI. 

Hermite  applied  this  preparation  to  sanitation. 

Chlorine  and  hypochlorites  fail  as  disinfectants  when  used  for 
materials  rich  in  dead  organic  matter.  Whilst  the  dead  matter  is 
being  oxidized,  the  germs  escape. 

Estimation  of  CI  in  Bleaching  Powder. — Prepare  a  decinormal 
solution  of  sodium  thiosulphate,  Na.^SoOg.sHaO.  Dissolve  24-827 
grammes  of  the  crystals  in  a  litre  of  H2O. 

Weigh  a  gramme  of  bleaching  powder,  and  grind  it  thoroughly  in 
a  mortar.  Add  small  quantities  of  water  at  a  time,  and  rub  into  a 
smooth  cream.  Decant  the  liquor  into  a  litre  flask.  Continue  to 
grind  the  sediment  with  successive  quantities  of  water  until  the 
whole  is  transferred  to  the  litre  flask  as  a  fine  emulsion.  ]\Iake  up 
to  the  mark. 

Take  20  c.c.  of  the  uniform  emulsion  in  a  basin;  add  excess  of 
KI  solution,  dilute  slightly,  and  acidify  with  acetic  acid.  Titrate 
the  liberated  I  with  ^^  thiosulphate  and  starch. 

One  c.c.  YzT  thiosulphate  =  0-0035 -4  gramme  CI. 


DISINFECTANTS  207 

Another  method:  Prepare  -j'^  I,  and  l^^-^  solution  of  .'ilk;ilin<; 
arsenite. 

Mix  commercial  rcsubHrncd  iodine  with  half  its  weight  KI,  and 
dissolve  in  half  its  weight  of  water.  Precipitate  the  I  with  water, 
and  filter  through  asbestos;  wash  well  to  remove  KI,  and  dry  over 
H2SO4.  Sublime  between  two  large  watch-glasses  twice,  and 
finally  weigh  out  12-7  grammes.  Dissolve  this  in  18  grammes  KI 
(pure)  and  about  250  c.c.  H^O.     Make  up  to  a  litre. 

Dissolve  4-95  grammes  pure  sublimed  and  powdered  ASgOg  with 
20  grammes  pure  sodium  carbonate  in  about  25,0  c.c.  HoO.  Warm 
and  shake  occasionally  until  solution  is  complete;  cool  and  make 
up  to  a  litre. 

Take  20  c.c.  of  the  well-shaken  turbid  emulsion  of  bleaching 
powder  in  a  basin,  and  run  in  from  a  burette  ~  arsenious  solution 
in  slight  excess  (a  drop  fails  to  produce  a  blue  stain  on  KI — starch 
paper).  Add  some  starch  and  run  in  ~  I  from  another  burette 
until  a  slight  blue  colour  remains.  The  number  of  c.c.  ~  I  required 
•gives  the  number  of  c.c.  of  arsenious  solution  that  have  been  added 
in  excess;  subtract  this  from  the  total  added  to  obtain  the  number 
■of  c.c.  of -j^  arsenious  solution  equivalent  to  the  CI  in  the  bleaching 
powder  used — 

One  c.c.  y{j  arsenious  solution  =  0-00354  gramme  available  CI. 

These  methods  determine  quantitatively  chlorinated  soda, 
Hermite  solution,  chlorine-,  bromine-,  and  iodine- water. 

Sulphur  Dioxide  in  Solution,  and  in  Sulphite — Estimation  in 
Solution. — Weigh  the  solution  (previously  cooled  to  5°  C.  in  a 
freezing  mixture)  in  a  stoppered  flask;  introduce  it  into  a  second 
•stoppered  flask,  containing  excess  ^  iodine.  Shake  thoroughly, 
and  estimate  the  unchanged  iodine  with  ^  thiosulphate  and 
.c'l"  o  Tpn 

SO2  +  I,  +  2H.,0  =  H^SOj  +  2HI. 

Each  c.c.  of  ^  I  taking  part  in  the  reaction  =  0-0032  gramme  SO.,. 

Estimation  in  Sulphite. — Powder  some  sulphite  finely.  Weigh  a 
small  quantity  in  a  watch-glass,  and  introduce  it  immediately  into 
a  measured  excess  of  -^jj  I  in  a  beaker.  Stir  until  the  reaction  is 
complete,  a  result  only  slowly  obtained  with  insoluble  sulphites — 


298  PRACTICAL  SANITARY  SCIENCE 

e.g.,  calcium  sulphite.  Estimate  the  excess  iodine.  It  is  well  to- 
do  a  second  determination,  using  only  a  slight  excess  of  -^^  I. 

The  SOo  is  calculated  as  above. 

Bromine  acts  in  a  similar  manner  to  chlorine  by  liberating  nascent 
oxygen.  Its  germicidal  power  in  the  free  state  has  been  estimated 
as  about  equal  to  that  of  chlorine,  but  in  combination  with  organic 
radicals  it  is  superior.  If  careful  comparative  tests  be  made,  how- 
ever, it  will  be  found  that  bromine  is  a  more  energetic  disinfectant 
than  chlorine,  and  more  energetic  than  can  be  accounted  for  by 
the  amount  of  nascent  O  liberated.  This  fact  leads  to  the  conclusion 
that  Br  acts  as  a  disinfectant  in  a  manner  other  than  by  liberating 
oxygen. 

Iodine  as  an  oxidizer  is  feebler  than  chlorine  or  bromine,  but 
destroys  bacteria  more  energetically  than  either  by  combining  with 
their  protoplasm. 

Matthews  found  that  a  solution  of  iodine  in  iodide  of  potassium 
of  a  strength  of  i  in  i,ooo  killed  an  emulsion  of  Staphylococcus^ 
Pyogenes  aureus  in  water  in  fifteen  seconds,  whilst  iodoform  in  full 
dose  was  without  action, 

Permangranate  of  potassium,  K20,Mn207,  when  acidified 
with  H0SO4,  can  yield  5  atoms  of  oxygen  to  organic  matter: 

KX>MryJdi  +  3H2SO4  =  K2SO4  +  2MnS04  +  3H0O  +  5O. 

If  insufficient  H.^SOj  be  used,  only  3  atoms  of  O  are  furnished : 

K.O.MngO,  +  H2SO4  +  sHgO^  K2SO4  +  2Mn(OH)4  +  3O. 

Like  the  other  oxidizing  disinfectants,  its  germicidal  powers  are 
expended  on  dead  organic  matter  and  inorganic  compounds,  such  as 
sulphuretted  hydrogen,  ferrous  salts,  nitrites,  etc.,  rather  than  on 
living  bacteria.  But  for  naked  bacteria  permanganates  are  power- 
ful disinfectants.  The  disinfectant  activities  of  oxidizers  are  in- 
creased by  the  addition  of  haloid  acids. 

Estimation  of  Potassium  Permanganate. — Prepare  y'y  oxalic  acid 
by  dissolving  6-301  grammes  pure  crystals  in  a  litre  of  water. 

On  adding  potassium  permanganate  to  a  warm  solution  of  oxalic 
acid  and  sulphuric  acid,  the  following  reaction  occurs: 

SHaC.O^,  2H2O  +  3H2SO,  +  2KMn04  = 

10CO2  +  K2SO4  +  2MnS04  +  18H2O. 


DISINFECTANTS  299 

The  factors  taking  part  in  oxidation  may  bo  written  more  simply: 
H2C204'2H20  +  0  =  2CO2  +  3H2O. 

Place  50  c.c.  of  the  fj^  oxalic  acid  and  a  little  H2SO4  in  a  beaker, 
and  dilute  with  water;  heat  to  60°  C.  Gradually  run  in  from  a 
burette  the  permanganate  solution  (about  5  grammes  to  the  litre) 
until  a  faint  permanent  pink  remains  in  the  liquid  after  stirring. 
If  the  permanganate  be  added  too  rapidly,  a  brown  precipitate  forms, 
which  is  removed  with  difficulty  by  adding  more  sulphuric  acid. 

One  c.c.  Y^  oxalic  acid  =  0-003163  gramme  potassium  perman- 
ganate. 

Salts  of  Mercury. — Of  metalHc  salts,  perchloride  of  mercury 
has  had,  perhaps,  a  larger  application  as  a  disinfectant  in  medicine 
and  surgery  than  all  the  others  put  together.  The  metalhc  ion  in 
solution  unites  with  the  protoplasm  of  the  germ,  causing  its  death. 
The  complex  appears  to  be  of  the  nature  of  a  precipitate  rather  than 
a  coagulum,  as  it  redissolves  in  excess  of  albumin.  It  is,  therefore, 
necessary  to  use  perchloride  of  mercury  in  excess.  The  salt  is  highly 
poisonous.  The  readiness  with  which  protoplasm  is  precipitated 
by  its  forming  albuminate  and  other  protein  compounds  of  mercury 
militates  against  it  as  a  disinfectant  for  sputum  rich  in  albuminoid 
matters,  or  for  abscess  cavities.  The  precipitated  coat  of  albumin 
protects  the  enclosed  bacteria  from  further  action ;  hence  the  germs 
can  survive,  and  on  breaking  down  of  the  pellicle  may  migrate  and 
set  up  infection  at  a  distance. 

The  cyanide  and  iodide  of  mercury  are  both  highly  germicidal 
and  highly  poisonous.  Mercury  salts  interfere  with  the  action  of 
soap. 

Mercuric  chloride  is  estimated  by  dissolving  it  in  HCl,  and  pre- 
cipitating the  sulphide  by  passing  HoS  to  saturation.  The  pre- 
cipitate is  allowed  to  stand  for  a  time,  then  thrown  on  a  filter  and 
washed,  until  the  washings  leave  no  residue  on  evaporation.  It 
is  then  dried  at  100°  C.  and  weighed.  Hg  is  calculated  from  the 
weight  of  the  HgS.  The  precipitate  may  contain  free  S,  in  which 
case  it  is  washed  with  recently  distilled  CS,,. 

Formaldehyde,  |t^C:0,  is  obtained  by  oxidizing  the  vapour 

of  methyl  alcohol  in  the  air  in  contact  with  heated  platinum  or 


300  PRACTICAL  SANITARY  SCIENCE 

copper,  and  receiving  the  products  in  water.  The  lonnahn  of  com- 
merce is  a  40  per  cent,  solution  of  the  aldehyde  in  water  and  methyl 
alcohol.  On  evaporating  this  solution  in  vacuo  in  the  presence  of  a 
small  amount  of  HjSO^,  a  crystalline  white  powder  falls  out,  of 
undetermined  molecular  weight  (CH.,0)„,  and  known  by  the  names 
'  paraformaldehyde  '  and  '  paraform.'  This  polymer  is  volatilized 
on  heating  into  formaldehyde.  Both  the  liquid  and  solid  forms  are 
used  in  disinfection.  An  enormous  amount  of  work  has  been  done 
on  the  properties  of  formaldehyde  as  a  germicide,  and  everyone  is 
agreed  that  as  such  it  holds  a  high  position.  For  application  to 
rooms  the  solution  may  be  heated,  or  the  solid  may  be  volatilized 
over  a  lamp.  There  can  be  little  doubt  that  the  interaction  between 
formaldehyde  and  the  protoplasm  of  the  germ  is  of  the  nature  of  a 
coagulation.  Its  powerful  reducing  properties  remove  oxygen  from 
the  protoplasm,  probabl}'  both  from  liydroxyl  groups  and  from  the 
oxygen  united  directly  to  carbon. 

It  is  used  for  the  floors,  walls  and  ceilings  of  rooms  as  a  spray, 
in  the  form  of  vapour  produced  by  an  autoclave  under  pressure,  and 
as  the  vapour  of  paraform  produced  by  a  lamp.  For  spray  work 
various  strengths  of  solution  have  been  recommended,  ranging  from 
0-5  per  cent,  to  2-5  per  cent,  and  higher.  Some  suggest  supple- 
menting the  spra}^  with  vapour,  more  especially  where  rooms  are 
exceptionally  dirty,  and  unknown  organisms  like  that  of  smallpox 
are  being  dealt  with.  In  the  present  state  of  practical  disinfection 
a  wide  margin  of  safety  should  be  insisted  on.  It  is  possible  that 
in  some  circumstances  the  highest  concentration  recommended  fails 
to  sterilize. 

Estimation  of  Formaldehyde. — Fonnaldehyde  slowly  absorbs  am- 
monia to  form  hexamethylene-tetramine;  180  parts  formaldehyde 
react  with  68  of  ammonia: 

6CH,0  +  4NH3  =  (CHoJeN^  +  6H.,0. 

Place  10  c.c.  of  the  solution  to  be  tested  in  a  flask,  and  neutralize, 
if  necessary,  with  ^^  NaOH ;  dilute  with  water,  and  treat  with  an 
excess  of  standard  ammonia  solution.  It  is  well  to  stand  over- 
night. Distil  the  excess  of  ammonia  b}^  a  current  of  steam  into 
standard  acid.  Calculate  the  percentage  amount  of  formaldehyde 
from  the  amount  of  ammonia  combined. 


DISINFEC TAN'I  S  30 1 

The  success  which  attended  the  early  apphcation  of  Carbolic  Acid 
as  an  antiseptic  by  Pasteur,  Lister,  and  others,  attracted  attention 
to  coal  tars  as  a  source  of  germicides. 

By  suitable  fractional  distillation  these  tars  can  be  separated 
into — (i)  First  runnings;  (2)  light  oils;  (3)  heavy  oils;  (4)  anthracene 
oils. 

Carbolic  acid  is  contained  for  the  most  part  in  the  light  oil 
fraction ;  whereas  the  heavy  oil  fraction  contains  its  homologues, 
especially  the  cresols. 

At  first  acid  and  alkaline  solutions  of  crude  carbolic  acid  were 
used  as  disinfectants,  but  it  was  soon  found  that  these  were  not 
suitable.  Pure  watery  solutions  of  cresols  were  then  tried,  and 
likewise  abandoned  for  saponified  emulsions.  It  was  discovered 
that  emulsions  conferred  increased  germicidal  efficiency  on  the 
various  active  phenolic  bodies  used,  and  that  side-chain  substitution 
in  the  benzene  ring  produced  the  same  result. 

It  was  also  discovered  that  metacresol,  the  least  soluble  in  water, 
had  a  higher  germicidal  power  in  emulsion  than  ortho-  or  para- 
cresol. 

The  relative  solubilities  of  the  three  isomers  in  water  are — 

Per  Cent. 

Orthocresol  . .  . .  . .  . .  . .     2-5 

Metacresol  . .  . .  . .  . .  . .     0-53 

Paracresol  . .  . .  . .  . ,  . .      i-8 

Two  important  stages  in  the  evolution  of  coal-tar  disinfectants 
had  now  been  reached  and  passed.  The  emulsion  was  better  than 
the  solution:  insolubility  in  water  was  of  advantage  in  the  same 
direction. 

The  high  germicidal  properties  of  thymol  illustrate  these  princi- 
ples, containing  as  it  does  three  side-chains  attached  to  the  benzene 
ring: 

/CH3   (I) 

CgHg— C3H7       (4) 

\0H     (3) 

Its  molecular  weight  is  much  higher  than  that  of  phenol(CgH5.0H). 
Its  solubility  in  water  is  about  i  in  1,100,  as  against  i  in  15  for 
phenol.     Koch  found  that  the  same  germicidal  work  was  performed 


302  PRACTICAL  SAXITARY  SCIENCE 

on  anthrax  bacilli  by  thymol  in  dilution  of  i  in  80,000  as  by 
phenol  in  i  in  1,250. 

Estimation  of  Phenols. — The  following  method  is  based  on  the 
precipitation  of  phenol  from  its  aqueous  or  alcoholic  solution  by 
bromine  as  tribromphenol. 

Prepare  a  standard  solution  consisting  of  2-04  grammes  sodium 
bromate  and  8-oo  grammes  potassium  bromide  in  a  litre  of  water. 

One  c.c.  of  this  solution  =  0-0012638  gramme  phenol. 
5KBr  +  NaBrOg  +  6HC1  =  5KCI  +  NaCl  +  3Br.,  +  3H2O. 
CgH^OH  +  3Br.,  =  QH^OHBrg  +  3HB"r. 
2KI  +  Br;=2kBr+L.' 
1,  +  j^^S.p'.  -  Na^SjOg  ;  2XaI. 

Weigh  out  a  gramme  or  two  of  the  phenol  to  be  tested  in  a  tared 
watch-glass,  and  dissolve  in  excess  of  NaOH.  Make  up  to,  say, 
500  c.c.  Take  20  c.c.  (one-twenty-fifth  of  the  whole)  in  a  300  c.c. 
stoppered  flask,  and  add  25  c.c.  of  the  standard  bromide  bromate 
solution.  In  a  second  300  c.c.  stoppered  flask  place  25  c.c.  of  the 
standard  bromide  bromate  solution. 

To  each  add  5  c.c.  pure  HCl  and  shake.  Add  such  a  further 
measured  quantity  of  the  standard  bromide  bromate  solution  to  the 
phenol  flask  that,  on  shaking,  the  white  tribromphenol  is  left  dis- 
tinctly yellow  (excess  Br).  Shake  well  and  stand  for  fifteen  minutes. 
Add  excess  KI  to  both  flasks,  and  titrate  with  a  solution  of  thio- 
sulphate  of  Na  (say  10  grammes  to  a  litre). 

Example. — 2-i68  grammes  phenol  required  75  c.c.  standard 
bromide  bromate  to  become  yellow.  The  iodine  which  the  free 
bromine  liberated  required  i6-8  c.c.  thiosulphate.  But  25  c.c. 
bromide  bromate  in  second  flask  required  51-8  c.c.  thiosulphate. 
Therefore  i6-8  c.c.  thiosulphate  =  8-i8  c.c.  bromide  bromate  solu- 
tion. Therefore  75 —8'i8  =  66-82  c.c.  bromide  bromate  solution 
which  interacted  with  phenol.  Therefore  66-82x0-0012638x25=: 
2-III  grammes  phenol. 

2-i68  :  2-111  ::  100  :  97-4. 

That  is,  this  sample  contains  97-4  per  cent,  pure  phenol. 
Laubenheimer  showed  that   a   i   per  cent,  solution  of  phenol 
required  ninety  minutes  to  kill  a  quantity  of  staphylococci,  whereas 


DISINFECTANTS  303 

the  same  strength  of  a  solution  of  propyl-phenol,  C^//  ^.Vr ''  did 

the  same  work  in  three  minutes. 

Increase  in  molecular  weight  does  not  always  mean  increase  in 
germicidal  power;  because,  in  the  same  series  of  Laubenheimer's 
experiments,  isopropyl-phenol  required  twelve  minutes  to  kill. 
Working  with  m-xylenol, 

/CH3  (I) 

CgHg-CH,,  (3) 

\0H    (5) 

S5niimetric,  and  ^-xylenol, 

/CH3  (I) 
CeH3-CH3  (4) 

\0H  (2) 

he  found  that  the  meta-compound  was  much  more  powerful  than 
the  para-  in  killing  staphylococci. 

On  incorporating  an  atom  of  chlorine  in  meta-  and  para-cresols, 
he  found  that  chlor-m-cresol, 

/CH3  (I) 
CgHa^OH   (3) 

\C1      (6)1 

still  retained  its  advantage,  and  even  increased  this  advantage  over 

chlor-/)-cresol, 

/CH3  (I) 
CeH3-0H    (4) 

\  CI      (2) 

The  relative  position  of  the  side-chains  in  the  ring  is  thus  shown 
to  be  of  importance.  It  may  very  well  be  that  the  disinfection 
process  is  assisted  by  the  meeting  of  suitable  side-chain  affinities 
in  microbe  and  disinfectant. 

Decrease  in  solubility  in  water  means  decrease  in  toxicity.  It  is 
possible,  therefore,  to  apply  to  the  skin  and  intestinal  mucosa 
■insoluble  phenyloids  in  concentrations  which  could  not  be  tolerated 
in  phenol. 

Henle,  working  twenty  years  before  Laubenheimer,  showed  that 
the  germicidal  powers  of  the  cresols  varied  with  their  boiling- 
points,  the  meta-compound,  with  highest  boihng-point,  possessing 


304  PRACTICAL  SANITARY  SCIENCE 

the  most  intense  action,  and  the  ortho-,  with  the  lowest  boiHng- 
point,  the  least  intense  action. 

Working  with  higher  phenols,  Sommerville  found  that  the  same 
principle  obtains.  Using  the  Rideal-Walker  method  of  estimating 
germicidal  efficiency,  and  emulsionizing  fractions  from  the  same 
distillate  of  blast-furnace  phenyloids,  he  found  that  a  fraction  boiling 
at  248°  possessed  a  coefficient  three  points  above  that  of  another 
fraction  boiling  at  220°,  and  five  points  above  that  of  a  third 
fraction  boiling  at  207°. 

Again,  it  is  possible  to  alter  by  several  points  the  coefficient  of  a 
phenyloid  by  varying  the  chemical  or  physical  characters  of  the 
emulsion. 

Changes  which  make  for  increased  adsorption  raise  (within  limits) 
the  coefficient.  Increased  viscosit}'  in  the  emulsion  lowers  (within 
limits)  the  coefficient. 

If  a  liquid  is  contained  between  two  parallel  plates,  and  one  of 
these  be  moved  with  a  constant  velocity  in  its  own  plane,  a  certain 
force  is  required  which  depends  on  the  velocity,  the  surface,  and 
distance,  of  the  two  plates,  and  on  the  temperature  and  nature  of 
the  liquid.  The  force  required  to  move  a  plate  of  unit  surface 
separated  from  another  plate  of  the  same  size  by  a  layer  of  liquid 
of  unit  thickness  at  unit  velocity  is  known  as  the  viscosity  coefficient. 

Colloidal  solutions  may  be  divided  into  two  classes  if  the  increase 
of  viscosity  compared  with  that  of  the  continuous  phase  (solvent) 
be  made  the  basis  of  classification.  One  class  presents  a  viscosity 
only  slightly  higher  than  that  of  water  (metal  and  sulphide  solu- 
tions). The  other,  the  organic  colloids  (albumin,  gelatin)  presents 
a  marked  increase  of  viscosit3^  In  those  solutions  presenting  a  low 
viscosity,  the  disperse  phase  is  present  as  solid  particles;  in  those 
with  high  viscosity,  the  disperse  phase  is  liquid.  Albumin  solu- 
tions consist  of  a  dilute  solution  of  albumin  in  which  are  dispersed 
globules  of  a  more  concentrated  solution.  Systems  of  solid  particles 
of  microscopic  size  distributed  in  a  liquid  are  known  as  '  suspen- 
sions ' ;  those  consisting  of  two  liquid  phases  are  known  as  '  emul- 
sions.' 

The  particles  in  a  solution,  if  sufficiently  small,  are  in  constant 
motion,  oscillating  round  a  central  position,  and  also  undergoing 
an  irregular  translatory  motion.     Svedberg  showed  that  the  ampli- 


DISINFECTANTS  305 

tude  of  the  motion  of  a  particle  is  directly  proportional  to  the  period, 
and  inversely  proportional  to  the  viscosity,  of  the  liquid.  Perrin 
showed  that  this  Brownian  movement  conformed  to  the  principles 
of  the  kinetic  theory,  and  that  the  particles  could  be  treated  as 
large  molecules.  The  stability  of  the  solution  is  intimately  con- 
nected with  the  electric  charge.  The  charge  can  be  altered  by  the 
addition  of  electrolytes,  and  may  fall  to  zero  with  suitable  con- 
centrations, in  which  last  case  the  solutions  precipitate.  It  has 
been  long  known  that  the  speed  of  settling  of  such  suspensions  can 
be  increased  by  the  addition  of  electrolytes. 

In  systems  of  two  liquid  phases,  it  can  be  shown  that  very  small 
liquid  particles  approaching  ultramicroscopic  dimensions  possess 
a  high  degree  of  rigidity.  Systems  of  two  liquid  phases  possessing 
few  and  widely  .separated  particles  differ  in  no  important  respect 
from  systems  containing  rigid  particles;  but  an  important  difference 
appears  as  the  amount  of  disperse  phase  per  unit  volume  increases. 
In  the  case  of  rigid  spherical  particles  in  contact,  the  disperse  phase 
may  reach  a  maximum  of  74  per  cent,  of  the  total  volume.  If  the 
disperse  phase  be  liquid,  the  globules  may  not  merely  touch  one 
another,  but  become  flattened  at  the  points  of  contact,  from  which 
circumstance    it    is  obvious  that  there  is  no  limit  to  the  ratio 

vol.  of  disperse  phase       u-  u      j.-  i,        v         tj.    • 

f — = — i- ,  which  ratio  may  approach   unity.      It    is 

total  vol.  J      rr  J 

not  possible  to  prepare  emulsions  containing  such  percentages  of 

disperse  phase  unless  the  continuous  phase  is  a  solution  of  certain 

substances,  such  as  soap.     Such  bodies  froth,  an  indication  that 

the  dissolved  substance  lowers  the  surface  tension  of  the  solvent. 

The  process  of  emulsification  is  intimately  connected  with  such 

lowering  of  surface  tension,  or,  rather,  interfacial  tension  between  the 

two  phases. 

The  stability  of.  emulsions  -varies  considerably.  They  are 
destroyed  by  the  addition  of  all  substances  which  destroy  the 
emulsifying  agent;  thus, "emulsions  made  with  soap  solution  are 
destroyed  by  the  addition  of  an  acid  which  decomposes  the  soap. 

In  the  making  of  an  emulsion,  -the  two  phases  are  shaken  up  until 
the  disperse  phase  is  sufficiently  finely  distributed.  In  the  case  of 
gelatin  emulsions  and  soap  emulsions,  the  behaviour  of  the  solution 
is  not  to  be  explained  unless  by  assuming  that  it  is  a  system  of  two 

20 


3o6  PRACTICAL  SANITARY  SCIENCE 

fluid  phases;  in  other  words,  it  consists  of  globules  having  a  high 
gelatin  content  in  a  continuous  phase  which  is  a  dilute  solution  of 
gelatin.  The  solvent  here  may  be  shifted  most  readily  from  one 
phase  to  the  other.  Different  behaviour  is  shown  by  the  albumins. 
Egg  albumin  is  soluble  in  water,  and  does  not  form  a  gel.  either 
by  cooling  or  concentration,  but  it  coagulates  irreversibly  at  a 
temperature  of  about  60°  C.  The  temperature  of  coagulation  can 
be  changed  b}'  adding  salts,  and  may  be  raised  to  over  100°  by 
the  addition  of  a  thiocyanate.  In  relation  to  this  phenomenon  is 
the  change  which  follows  the  addition  of  alkali  salts  in  the  cold — 
the  coagulation  known  as  '  salting  out.' 

If  at  the  boundary  surface  between  the  phases  of  a  disperse 
system  a  change  in  the  concentration  of  either  phase  will  lead  to  a 
decrease  of  surface  tension,  this  change  will  occur.  The  change  in 
concentration  is  adsorption.  It  requires  work  to  make  or  enlarge 
a  surface;  when  such  surface  is  made,  it  is  the  seat  of  energy.  As 
we  have  seen  above,  adsorption  plays  probably  an  important  role 
in  disinfection.  Soap  emulsions  of  coal-tar  phenyloids  can  be  con- 
structed which  are  eminently  suitable  for  the  production  of  this 
phenomenon.  Such  emulsions  when  compared  with  suspensions 
show  a  decreased  size  of  particle  with  reduced  velocitj'  of  settlement, 
increased  Brownian  movement  with  increased  electric  charge,  due  to 
the  great  increase  of  specific  surface.  These  emulsions  provide  for 
a  high  degree  of  bombardment  of  the  microbe  by  the  active  par- 
ticles of  disinfectant,  followed  by  marked  adsorption,  both  necessary 
preliminaries  to  the  final  chemical  action  required  to  kill  the 
organism. 

In  most  of  the  modern  better-class  disinfectants  distilled  from 
tar,  and  emulsionized  in  soaps,  the  active  principles  are  phenyloids. 
In  the  raw  materials  these  bodies  are  mixed  with  neutral  oils, 
saturated  paraffins,  unsaturated  paraffins  (olefines,  etc.),  pyridines, 
and  a  mass  of  heterogeneous  substances. 

The  unsaturated  hydrocarbons  are  washed  out  with  H2SO4,  and 
the  phenyloids  with  NaOH  (formation  of  sodium  phenylates). 
Separation  is  made  in  laboratory  practice  in  separator  funnels. 
The  addition  of  a  few  drops  of  alcohol  sometimes  assists  the  separa- 
tion. 

Sodium  phenylates  are  spht  with  H2SO4,  and  the  free  phenyloids 


DISINFECTANTS  307 

recovered.  These  may  be  fractionally  distilled,  and  the  fractions 
emulsionized.  Hard  waters,  including  sea-water,  '  salt  out '  soap 
emulsions  in  varying  degrees.  Such  waters  should  be  softened 
before  using  them  for  diluting  soap  emulsions  of  phenyloids. 
Gelatin  or  glue,  whilst  not  forming  so  good  an  emulsion  as  soaps, 
is  not  attacked  by  hard  waters  to  the  same  degree. 

To  determine  the  percentage  composition  of  a  coal-tar  disinfectant 
in  a  soap  emulsion,  fractionally  distil  100  grammes  of  the  disin- 
fectant. Measure  the  water  and  weigh  the  phenyloids.  Below 
270°  C.  resin  gives  no  trouble,  as  any  resin  spirit  present  (never  more 
than  5  per  cent,  in  resin  soap)  is  in  union  with  alkali,  and  resin  oils 
boil  between  300°  and  400°  C.  Should  a  small  quantity  of  neutral 
oil  come  over,  which  rarely  happens,  it  may  be  separated  with  the 
phenolic  bodies  by  washing  with  soda,  and  subsequently  splitting  off 
the  phenyloids  with  H2SO4. 

Five  grammes  of  the  disinfectant  are  incinerated,  resulting  in 
NagCOg  or  KgCOg.  The  residue  is  lixiviated  with  water,  filtered, 
titrated  with  standard  HCl,  and  calculated  as  NagO  or  KgO.  The 
weight  of  the  chloride  will  at  once  determine  whether  one  is  dealing 
with  K  or  Na. 

As  the  residue  in  the  distillation  retort  consists  of  anhydrides  of 
fatty  acids  or  resin  acids,  or  of  both,  of  the  form 


R.  CO 


ONa 


R.  COO     Na 


it  is  plain  that  in  the  original  disinfectant  those  anhydrides  plus 
H2O  are  equivalent  to  the  NagO.  Hence  5  grammes  disinfectant 
minus  weight  of  NagO  equals  fatty  acids  plus  resin  in  5  grammes. 
If  the  fatty  acid  and  resin  figures  are  required  separately,  they  can  be 
easily  worked  out  from  the  retort  residue  by  Twitchell's  method. 

In  1903  Rideal  and  Walker  published  a  method  of  standardizing 
disinfectants.  The  method  has  since  undergone  slight  modifica- 
tions, and  to-day  is  carried  out  as  follows:  The  materials  required 
for  the  test  are  a  standard  nutrient  bouillon,  standard  carbolic 
acid,  dilution  of  the  disinfectant,  and  the  broth  culture.  The 
nutrient  bouillon  is  composed  of  20  grammes  of  Liebig's  extract  of 


3o8  PRACTICAL  SAXITARY  SCIENCE 

meat,  20  grammes  of  \\'itte's  peptone,  10  grammes  of  sodium 
chloride,  and  i  litre  of  distilled  water.  This  mixture  is  boiled 
for  thirt}^  minutes,  filtered,  and  neutralized  with  normal  sodium 
hydrate,  using  phenolphthalein  as  indicator.  To  avoid  contamin- 
ating the  broth  with  phenolphthalein,  a  small  aliquot  part,  say 
10  c.c,  should  be  taken  out  and  titrated  with  y^^  NaOH;  from  the 
result  obtained  a  calculation  is  made  of  the  amount  of  nonnal 
sodium  hydrate  necessary  for  the  neutralization  of  the  remainder 
of  the  broth.  When  quite  neutral,  15  c.c.  of  N.HCl  is  added.  The 
broth  is  then  made  up  to  a  litre  and  sterilized.  Where  2  or  3  htres 
are  prepared  at  one  time,  as  is  customary,  the  broth  is  distributed 
in  500  c.c.  flasks  on  the  following  day  and  again  sterilized.  With 
the  aid  of  a  small  separating  fvmnel,  5  c.c.  are  then  run  into  sterile 
test-tubes,  which,  after  plugging  with  sterile  cotton-wool,  are  placed 
in  the  steam  sterilizer  for  half  an  hour. 

As  carbolic  acid  crystals  are  frequently  contaminated  by  cresols 
to  such  an  e.xtent  as  to  make  them  unreliable  for  purposes  of 
bacteriological  control,  their  purity  should  be  established  by  a 
determination  of  the  solidifying-point  on  at  least  50  c.c.  of  material 
with  the  thermometer  in  the  liquid.  The  point  is  very  sharp,  the 
thermometer  showing  a  constant  temperature  for  a  period  of  from 
five  to  ten  minutes.  The  sohdifying-point  of  the  crystals  is  40-5, 
but  anything  over  40  may  be  accepted.  A  50  per  cent,  by  weight 
stock  solution  is  then  prepared  and  standardized  by  titration  with 
decinormal  bromine.  From  this  solution,  which  keeps  indefinitely 
in  stoppered  bottles,  the  various  working  strengths  are  made  by 
diluting  a  comparatively  large  quantity,  such  as  100  c.c,  to  the 
desired  volume;  this  serves  to  eliminate  the  error  introduced  by 
measuring  out  small  quantities  of  strong  acid. 

In  preparing  dilutions  of  the  disinfectant,  a  stock  solution  or 
emulsion  should  be  prepared  in  a  100  c.c.  stoppered  cylinder  with 
sterilized  distilled  water — 10  per  cent,  if  the  coefficient  be  under  r, 
and  I  per  cent,  if  over  i.  Ten  c.c.  of  this  stock  are  used  in  preparing 
each  of  the  four  dilutions  required  for  the  test.  Thus,  working  with 
a  sample  having  a  coefficient  under  i,  if  it  is  desired  to  prepare  a 
dilution  i  in  70,  10  c.c.  of  the  10  per  cent,  stock  solution  are  diluted 
with  60  c.c.  of  distilled  water ;  and  in  the  case  of  a  preparation  having 
a  coefficient  over  i,  where  the  dilution  required  is  i  in  700,  10  c.c. 


DISINFECTANTS  309 

of  the  I  per  cent,  stock  solution  should  be  diluted  with  60  c.c. 
water. 

•  The  culture  of  B.  typhosus  is  incubated  for  twenty-four  hours  at 
37°  C.  in  Rideal-Walker  broth.  It  is  advisable  to  make  a  sub- 
culture every  twenty-four  hours  from  the  previous  twenty-four- 
hour  culture,  even  if  on  many  days  no  test  is  performed ;  but,  as  this 
tends  to  attenuate  the  organism,  it  should  be  continued  for  not 
longer  than  one  month,  when  a  fresh  subculture  in  broth  should  be 
taken  from  an  agar  culture  one  month  old.  This  procedure  secures 
a  test  culture  varying  but  little  from  day  to  day  in  resistance  offered 
to  disinfectants,  and  renders  the  selection  of  the  appropriate  dilution 
of  carbolic  acid  easier  than  if  the  culture  from  which  the  twenty-four- 
hour  growth  is  obtained  were  older  on  one  occasion  than  on  another. 

The  apparatus  required  consists  of  a  test-tube  rack,  an  inoculating 
needle,  test-tubes,  and  a  dropping  pipette.  The  test-tube  rack 
possesses  two  tiers,  the  upper  having  holes  for  thirty  test-tubes  in 
two  rows,  each  row  containing  three  sets  of  five.  The  upper  tier 
holds  sterilized  broth  tubes,  each  of  which  is  numbered  with  a  grease 
pencil.  The  lower  tier  holds  the  medication-tubes,  four  containing 
the  postulant  disinfectant  dilutions,  and  one  the  carbolic  acid  con- 
trol dilution.  This  tier  is  provided  with  a  copper  water-bath 
intended  to  preserve  the  temperature  of  medication  within  the 
prescribed  limits  (15°  C.  to  18°  C).  The  test-tubes  are  numbered 
in  rotation;  and  it  will  be  seen  that  the  first  medication- tube  is 
used  for  inoculating  broth-tubes — i,  6,  11,  16,  21,  and  26;  the 
second  for  inoculating,  2,  7,  12,  17,  22,  and  27,  etc. 

The  needle  recommended  is  a  thin  aluminium  rod  carrying  a 
short  piece  of  platinum  wire,  o-oi8  inch  in  diameter  (26  U.S.  gauge), 
passed  through  and  twisted  round  an  eye  in  the  end  of  the  rod. 
A  loop  3  millimetres  internal  diameter  is  formed  on  the  end  of  the 
wire.  The  length  of  the  wire  to  the  end  of  the  loop  should  be  about 
if  inches.  A  fairly  uniform  drop  can  be  obtained  after  a  little 
practice  by  dipping  the  needle  in  the  medicated  culture,  and  bring- 
ing it  out  with  a  slight  jerk. 

The  test-tubes  should  be  of  strong  glass,  so  as  to  minimize  the 
risk  of  breakage,  and  lipped  to  facilitate  the  manipulation  of  plugs. 
The  size  recommended  is  5  inches  by  f  inch. 

The  cotton-wool  plugs  for  both  medication-tubes  and  broth-tubes 


3IO  PRACTICAL  SAXITARY  SCIENCE 

should  be  well  made,  so  that  they  can  be  withdrawn  and  replaced 
without  loss  of  time. 

The  dropping  pipette  is  standardized  to  deliver  o-i  c.c.  of  the 
broth  culture  per  drop.  It  is  loosely  plugged  at  the  top  with  cotton- 
wool, and  when  not  in  actual  use  is  kept  in  a  sterile  test-tube  plugged 
at  the  mouth  with  cotton-wool.  For  greater  convenience,  the  tube 
should  be  passed  through  the  centre  of  the  plug,  and  fastened  thereto 
with  wire.  In  addition  to  these,  one  or  two  of  each  of  the  following 
are  required:  i,  5,  and  10  c.c.  pipettes;  100  and  250  c.c.  stoppered 
cylinders,  with  inverted  beakers,  to  safeguard  against  dust  after 
removal  from  sterilizer;  wire  baskets  to  receive  tubes  for  incubation 
or  sterilization.     All  pipettes  and  cylinders  should  be  standardized. 

Before  commencing  the  test,  it  is  necessar}^  to  ascertain  the  car- 
bolic acid  control  dilution  which  will  give  the  desired  result — i.e., 
life  in  two  and  a  half  and  five  minutes.  This  is  done  by  running  a 
trial  test  with  five  dilutions  of  the  carbolic  acid  only — say  i  in  80, 
I  in  90..  I  in  100,  i  in  no,  and  i  in  120.  Five  c.c.  of  the  control 
solution  so  ascertained  are  then  pipetted  into  the  fifth  medication- 
tube,  the  other  four  receiving  5  c.c.  of  the  various  dilutions  of  the 
disinfectant  under  test.  To  save  time  and  apparatus,  one  pipette 
can  be  made  to  do  service  at  this  stage  by  starting  with  the  phenol 
solution,  and  following  on  with  the  highest  or  lowest  dilution  of  the 
disinfectant,  according  as  the  coefficient  is  below  or  above  i,  rinsing 
out  the  pipette  in  each  case  with  the  next  dilution  before  measuring 
off  the  sample  for  test. 

The  plug  of  the  culture-tube  is  now  replaced  by  the  culture  pipette, 
which,  as  explained  above,  has  a  plug  attached  to  it  with  wire, 
at  such  a  height  that,  when  the  plug  fits  easily  into  the  mouth  of 
the  culture-tube,  the  point  of  the  pipette  is  halfway  down  the 
broth,  and  clear  of  the  clumps.  The  first  of  the  five  medication- 
tubes  is  now  inoculated  with  five  drops  of  the  culture — i.e.,  0-5  c.c. 
At  intervals  of  half  a  minute  each  of  the  other  medication-tubes  is 
inoculated  in  turn.  By  the  time  the  fifth  tube  has  been  inoculated, 
the  organism  in  the  first  will  have  been  exposed  to  the  action  of 
the  disinfectant  for  two  minutes,  and  after  the  next  half-minute  a 
loopful  of  the  latter  is  inoculated  into  the  first  broth-tube,  loopsful 
from  the  other  medication-tubes  being  in  turn  inoculated  into  their 
respective  broth-tubes  at  the  rate  of  one  everj^  thirty  seconds.     By 


DISINFECTANTS  311 

the  time  the  fifth  broth-tube  has  been  inoculated  from  the  fifth 
medication-tube,  the  disinfectant  in  the  first  medication-tube  will 
have  acted  on  the  test  organism  for  four  and  a  half  minutes,  and 
after  the  next  thirty  seconds  a  loopful  is  introduced  into  broth-tube 
6,  and  so  on.  The  actual  test,  therefore,  occupies  seventeen  minutes, 
and  provides  for  six  two-and-a-half-minute  periods  of  contact  in  each 
of  the  five  medication-tubes. 

It  is  open  to  the  worker  to  adopt  any  convenient  method  of 
manipulating  the  tubes  and  plugs.  The  following  procedure  is  given 
for  the  guidance  of  the  inexperienced:  The  first  medication-tube  is 
taken  from  the  rack,  and  the  contents  gently  agitated  for  a  second 
to  insure  even  distribution  of  the  bacilli;  the  plug  having  been 
taken  out  and  grasped  by  the  left  little  finger,  the  tube  is  held 
between  the  back  of  the  left  forefinger  and  front  of  the  second.  The 
corresponding  broth-tube  (No.  i)  is  taken  up  by  the  right  hand  and 
transferred  to  the  left  between  the  thumb  and  forefinger,  the  plug 
being  extracted  and  held  by  the  little  finger  of  the  right  hand. 
The  tubes  now  being  in  position  for  inoculation,  the  needle,  which 
should  have  been  sterilized  before  the  tubes  were  touched,  is  intro- 
duced into  the  medication-tube,  from  which  a  loopful  is  taken  and 
inoculated  into  the  broth-tube.  The  needle  is  sterilized  in  the  flame 
(placed  to  the  right),  and  pushed  with  a  movement  of  the  thumb 
well  up  between  the  first  and  second  fingers  of  the  right  hand ;  the 
plugs  are  then  replaced,  the  medication-tube  going  back  to  the  rack, 
while  the  broth-tube  is  subjected  to  a  gentle  agitation  and  placed 
in  a  wire  basket  on  the  right  of  the  rack.  This  basket,  containing 
the  thirty  inoculation-tubes  and  test  form,  giving  particulars  of  the 
dilutions,  etc.,  is  now  placed  in  the  incubator,  where  it  is  allowed 
to  remain  for  fort\^-eight  hours  at  blood  heat,  when  the  results  are 
read  off.  A  moment's  consideration  of  the  manner  in  which  the 
test  has  been  conducted  will  suffice  to  indicate  where  the  results 
of  each  subculture  should  be  placed  in  the  table. 

The  following  details  of  a  test  of  a  disinfectant  marked  '  A  ' 
show  the  form  in  which  the  results  are  set  out ;  incidentally  it  shows 
the  degree  of  refinement  to  which  the  test  can  be  carried  wdth  a 
little  practice  and  care. 

The  strength  or  efficiency  of  the  disinfectant  under  test  is  ex- 
pressed in  multiples  of  carbolic  acid,  and  is  obtained  by  dividing 


3i; 


PRACTICAL  SAXITARY  SCIENCE 


the  dilution  of  the  disinfectant  showing  Hfo  in  two  and  a  half  and 
live  minutes  by  the  carboHc  acid  dikition,  which  of  course  must 
show  the  same  result.  In  the  present  instance  this  '  figure  of  merit,' 
or  Rideal- Walker  coefficient,  is  i6-6. 

,  To  avoid  annoyance  and  loss  of  time  caused  by  aerial  contamina- 
tion of  tubes,  etc.,  it  is  advisable  to  conduct  the  test  in  a  room  free 
from  draughts;  a  further  safeguard  is.  provided  by  spraying  or 
swabbing  the  floors  and  benches  with  an  efficient  disinfectant  solu- 
tion. Needless  to  add,  all  pipettes,  etc.,  must  be  rigorously 
sterihzed  before  use. 

In  this,  as  in  all  other  arbitrary  tests,  the  need  for  strict  observa- 
tions of  the  conditions  of  the  test  is  imperative. 


B.  Typhosus:  Twenty-four  Hours'  Broth  Culture  at  37°  C. 
Temperature  of  medication  15°  C.  to  iS°  C. 


Sample. 

Time  Culture  exposed  to  Action  of 
Disinfectants  (Minutes). 

Subcultures. 

2j. 

X 
X 
X 
X 
X 

5- 

X 
X 
X 
X 

7J- 

X 

X 

10. 

X 

12^. 

•5- 

Period  of 
Incubation. 

Tempera- 
ture. 

A 
Carbolic  acid 

1,900 
2,000 
2,100 
2,200 
120 

48  hours 

37°  C. 

.*.  Rideal-Walker  coefficient 


:i6-6. 


APPENDIX 

Flock  manufactured  from  rags,  to  be  used  in  upholstery,  bedding, 
etc.,  must  meet  the  standard  of  cleanliness  laid  down  by  the  Local 
Government  Board's  Rag  Flock  Regulations,  191 2 — viz.,  not  to 
contain  more  than  30  parts  chlorine  per  100,000  parts  flock,  the 
chlorine  to  be  removed  as  chlorides  with  distilled  water  at  a  tempera- 
ture not  exceeding  25°  C.  from  not  less  than  40  grammes  of  a  well- 
mixed  sample  of  flock. 

Steep  50  grammes  of  a  mixed  sample  of  flock  in  |  litre  of  dis- 
tilled water  overnight.  Decant  the  fluid  on  a  filter,  and  squeeze 
out  the  flock  thoroughly.  Wash  the  flock  with  smaller  quantities 
of  water  (say  100  c.c.)  three  or  four  times,  squeezing  out  all  the 
water  possible  each  time,  and  passing  the  washings  through  the 
same  filter.  Makeup  the  filtrate  to  a  litre.  Now  evaporate  100  c.c. 
of  this  (  =  5  grammes  flock)  to  dr^mess  with  a  small  quantity  of 
CaO  in  a  platinum  dish,  and  char  the  residue.  When  cool,  extract 
with  50  to  100  c.c.  distilled  water  and  filter.  Add  a  few  drops  of 
potassium  chromate  to  the  filtrate,  and  run  in  from  a  burette  silver 
nitrate  solution  (used  in  estimation  of  CI  in  water),  i  c.c.  of  which 
equals  i  milligramme  CI.  Multiply  the  number  of  c.c.  used  by  20 
to  obtain  parts  CI  per  100,000  flock. 


Copper  Sulphate  is  used  for  greening  peas  and  other  vegetables : 
Estimation  of  Copper. — Ash  10  grammes  of  the  peas  or  other 
material.  Moisten  the  ash  with  concentrated  HNO3;  add  water, 
and  boil.  Make  strongly  alkaline  with  ammonia,  and  filter.  If 
no  blue  colour,  copper  is  absent.  If  blue,  transfer  the  fluid  to  a 
Nessler  glass  on  a  white  tile,  and  match  the  colour  against  weighed 
small  quantities  of  copper  sulphate  converted  into  ammoniacal  solu- 
tion in  the  same  manner. 

Or,  the  copper  may  be  deposited  in  the  metallic  state  by  passing 
an  electric  current  through  the  acid  solution,  in  a  suitable  apparatus, 
and  weighed  as  Cu. 

Tin  in  Canned  Food. — See  Local  Government  Board  Reports 

of  Inspector  of  Foods,  No.  7;  Report  of  Buchannan  and  Schny'ver. 

313 


314  PRACTICAL  SANITARY  SCIENCE 

I.  Colorimetric  Method. — Prepare  a  solution  of  stannous  chloride 
containing  0-286  gramme  per  100  c.c. 

Prepare  a  solution  of  dinitrodiphenylaminesulphoxide  containing 
0*2  gramme  in  100  c.c.  ,^^  NaOH.  Mix  10  parts  HNO3  (sp.  gr.  1-48) 
with  10  parts  HXO;,  (sp.  gr.  1-4).  Cool  this  mixture  with  ice,  and 
add  I  part  of  thiodiphenylamine  (prepared  by  heating  diphenyl- 
amine  with  sulphur)  in  small  quantities  at  a  time  with  constant 
stirring.  Do  not  allow  the  temperature  to  rise  above  5°  C,  and 
add  such  small  quantities  at  a  time  that  a  hissing  sound  is  hardly 
perceptible  when  the  solid  comes  into  contact  with  the  liquid  mix- 
ture. The  thiodiphenylamine  dissolves  at  the  beginning  to  form  a 
clear  solution  of  red  colour,  which,  before  the  whole  of  the  amine 
has  been  added,  commences  to  thicken,  owing  to  the  separation  of 
the  nitro-body.  After  standing  for  some  hours  (not  more  than 
half  a  day),  suck  off  the  nitro-body  on  an  asbestos  filter,  and  wash 
first  with  concentrated  HNO3,  then  with  acid  of  gradually  dimin- 
ished strength,  and  finally  with  pure  water.  Now  extract  it  with 
hot  alcohol  in  which  it  is  not  appreciably  soluble. 

Introduce  10  grammes  of  the  food  into  a  700  c.c.  Kjeldahl  ffask- 
add  10  grammes  of  potassium  sulphate  and  10  c.c.  concentrated 
sulphuric  acid.  Heat  over  small  flame  till  mixture  chars  and  froths. 
Add  another  10  c.c.  H2SO4,  and  regulate  the  size  of  the  flame  so- 
that  the  H2SO4  can  be  boiled  without  loss  from  frothing.  Heat 
till  the  contents  of  the  flask  are  quite  white.  Cool;  dilute  with 
water  to  about  100  c.c.  Pass  in  H2S  gas,  and  let  stand  in  a  corked 
flask  overnight.  Warm  slightly  on  a  water-bath,  and  filter  off  the 
precipitated  sulphide  and  sulphur.  Transfer  the  filter-paper  con- 
taining the  precipitate  to  a  test-tube,  and  boil  with  5  c.c.  concen- 
trated HCl  to  dissolve  the  sulphide.  Filter  through  a  small  conical 
Buchner  funnel  into  a  wide-mouthed  test-tube,  with  a  side-tube 
near  the  top  to  connect  with  a  pump.  Suck  as  dry  as  possible,  and 
wash  with  2*5  c.c.  concentrated  HCl.  Connect  the  wide-mouthed 
test-tube  with  a  CO2  generating  apparatus,  and  pass  the  gas  through 
a  tube  which  passes  through  a  cork  inserted  in  the  mouth  of  the  test- 
tube,  and  which  reaches  nearly  to  the  surface  of  the  liquid.  The 
side-tube  serves  as  an  exit  for  the  gas.  Whilst  still  hot,  throw  into 
the  strongly  acid  liquid  a  strip  of  zinc  foil  2  inches  long,  0-5  inch 
wide,  and  weighing  about  075  gramme,  and  the  stannic  chloride  is 
reduced  to  stannous  chloride.  As  soon  as  the  last  traces  of  Zn  are 
dissolved,  add  2  c.c.  of  the  reagent  by  pipette  to  the  hot  liquid,  the 
CO2  passing  the  while.  On  addition  of  the  reagent,  the  nitro-body 
is  precipitated.  On  warming,  it  passes  again  into  solution  in  the 
concentrated  acid.  Boil  the  solution  for  a  minute  or  two,  and  dilute 
to  100  c.c.  with  cold  water.  Filter  the  dilute  solution  by  means  of 
a  pump  from  the  unchanged  nitro-body.  The  solution  usually  turns 
violet  during  filtration ;  the  full  depth  of  colour  is  rapidly  attained 


APPENDIX  315 

by  addition  of  a  drop  of  dilute  ferric  chloride.     It  is  tlien  iTiatf;lied 
with  known  quantities  of  the  standard  tin  solution.  | 

2.  Gravimetric  Estimation. — Fifty  granames  of  th(;  food  are  in- 
cinerated in  two  lots  of  25  grammes  in  two  Kjeldahl  flasks  of  about 
700  c.c.  capacity,  using  25  c.c.  of  H2SO4  previously  diluted  with 
100  c.c.  water,  and  25  grammes  potassium  sulphate.  When 
thoroughly  charred,  another  25  c.c.  concentrated  H2SO4  are  added, 
and  heat  continued  till  contents  are  white  (perhaps  four  to  five  hours 
required).  The  contents  of  the  two  flasks  are  brought  together  and 
diluted  to  about  600  c.c.  H2S  gas  is  passed,  and  the  mixture 
allowed  to  stand  corked  overnight.  It  is  next  warmed,  and  the 
mixture  of  sulphide  and  sulphur  filtered  through  a  small  filter-paper 
7  centimetres  in  diameter.  The  precipitate  is  washed  on  the  filter- 
paper  with  warm  water.  With  it  are  usually  mixed  bodies  other 
than  sulphur  and  sulphide,  such  as  silica  derived  from  the  flask,  etc. 
To  separate  these,  the  sulphide  is  dissolved  on  the  filter-paper  in 
a  small  quantity  (10  to  20  c.c.)  of  hot  10  per  cent.  NaOH.  From 
the  yellow  solution  obtained  the  sulphide  is  reprecipitated  by 
glacial  acetic  acid,  filtered  off,  washed  with  hot  water,  dried, 
oxidized,  and  weighed  as  oxide  of  tin. 


Estimation  of  Orgranic  Matter  in  Air.— In  addition  to  the 
microscopic  examination  of  dust  and  suspended  matters  in  the  air 
described  at  p.  143,  it  may  be  necessary  in  certain  cases  to  estimate 
organic  matter  quantitatively.  This  may  be  roughly  done  thus: 
Aspirate  a  measured  volume  of  air  through  a  tube  containing  a 
plug  of  clean  glass-wool,  and  digest  the  wool  in  standard  potassium 
permanganate  (p.  48)  for  an  hour  at  37°  C.  Titrate  the  perman- 
ganate with  standard  oxalic  acid  (07875  gramme  crystals  to  a  litre). 
Perform  a  blank  experiment,  and  deduct  the  number  of  c.c.  oxalic 
acid  used  from  that  used  in  the  actual  estimation.  The  result  is 
recorded  in  terms  of  O  absorbed  from  permanganate,  i  c.c.  oxalic 
acid  =  I  c.c.  permanganate  =  0-1  milligramme  O. 


Haldane's   Apparatus   for  Estimating-  CO 2  in  the  Air.— 

This  consists  of  an  air  burette  (enclosed  in  a  water-jacket  with  a 
glass  face)  with  a  wide  ungraduated  and  a  narrow  graduated  portion. 
Its  capacity  is  20  c.c.  from  top  to  bottom  of  scale.  The  graduated 
portion  measures  4  inches  in  length,  and  is  divided  into  100  equal 
parts,  each  corresponding  to  one-ten-thousandth  part  of  the  capacity 
of  the  burette  when  moist  for  mercury.  Readings  are  recorded  in 
parts  per  10,000  without  calculation  or  corrections.  The  water  in 
the  water-jacket  is  stirred  up  occasionally  in  order  to  secure  uni- 
formity of  temperature. 


3i6  PRACTICAL  SANITARY  SCIENCE 

In  using  the  apparatus,  the  air  is  tirst  expelled  by  a  three-way  tap 
from  the  burette  by  raising  the  mercury  bulb  attached  to  its  lower 
end.  Air  is  then  taken  in  by  lowering  tlie  bulb  till  the  mercury  falls 
to  the  zero  of  the  graduated  scale.  The  tap  to  the  absorption  pipette 
(the  latter  filled  to  a  mark  with  lo  per  cent.  KOH)  is  next  opened, 
and  the  air  is  driven  over  and  drawn  back  several  times  till  all  CO2 
is  absorbed  as  indicated  by  constant  level  of  Hg.  The  difference 
between  the  first  and  last  readings  gives  the  amount  of  CO2  in  parts 
per  10,000. 

Estimation  of  Formaldehyde  in  Meat  Foods. — See   Local 

Government  Board  Food  Reports,  No.  *.).  Scliry\er  points  out  that 
in  meat  foods  it  is  possible  that  the  formaldehyde  may  be  entirely 
oxidized  to  COo  and  HoO  by  tissue  oxidases;  that  part  of  the  fomi- 
aldehyde  may  be  polymerized  to  paraformaldehyde;  and  that 
formaldehyde  may  enter  into  chemical  combination  with  some  of  the 
constituents  of  the  foodstuffs.  He  has  confirmed  the  statement 
made  by  Cervello  and  Pittini,  and  by  Batelli  and  Stern,  that  forni- 
aldehyde  is  destro\'ed  by  tissue  oxidases. 

When  fomialdeiiyde  solution  is  distilled,  the  distillate  contains 
less  aldehyde  than  the  original  solution,  due  to  polymerization  by 
heat  into  a  non-volatile  pohTner.  It  is  therefore  not  possible  to 
estimate  formaldehyde  by  steam  distillation. 

.  Schiff  and  Sdrensen  have  shown  that  formaldehyde  reacts  with 
proteins  and  amino-acids,  with  formation  of  methylene-imino  com- 
pounds, and  that  the  reaction  is  a  reversible  one,  and  only  proceeds 
to  completion  in  presence  of  large  excess  of  formaldehyde : 

'  (NH2)CH2.COOH  +  HCHO  ^ > CHg :N.CH2.C00H  +  H.O. 

Amino-acids,  owing  to  basic  and  acidic  groups,  have  an  ampho- 
teric reaction,  and  become  acid  on  treatment  with  formaldehyde: 
the  number  of  amino-groups  in  combination  can  be  accordingly 
determined  by  titration  with  alkali.  Conversely,  it  is  possible  by 
titration  to  estimate  the  amount  of  formaldehyde  which  can 
enter  into  combination  with  anv  product.  Meats  contain  rela- 
tively large  quantities  of  substances  which  are  capable  of  entering 
into  chemical  combination  with  the  aldehyde.  The  reaction,  as 
already  mentioned,  will  not  proceed  to  full  completion  except  in 
presence  of  excess  of  aldehyde,  owing  to  the  reversibility. 

In  addition  to  these  reversible  compounds,  formaldehyde  can 
combine  with  proteins  to  form  relatively  stable  insoluble  products, 
irom  which  formaldehyde  can  be  eliminated  only  by  prolonged 
heating  with  water. 

Any  effective  method  for  estimating  formaldehyde  in  meat  must 
therefore  be  applicable  to  estimation  of  free  aldehyde,  the  poly- 
merized product,  and  aldehyde  in  combination  with  the  meat. 


APPENDIX  317 

The  violet  colour  obtained  when  milk  containing  fonnalflehyde 
is  heated  with  strong  HCl  in  the  presence  of  an  oxidizing  agent 
cannot  be  used  to  detect  aldehyde  in  meat,  as  meat  gives  a  violet 
colour  on  warming  with  HCl  in  the  absence  of  the  aldehyde  due 
to  the  formation  of  haematoporphyrin  from  haemoglobin. 
■     The  following  method  is  recommended : 

To  10  c.c.  of  solution  containing  aldehyde  add  2  c.c.  of  a  freshly 
prepared  and  filtered  i  per  cent,  solution  of  phenylhydrazine  hydro; 
chloride.  To  this  add  i  c.c.  of  a  5  per  cent,  fresh  potassium  ferri- 
cya.nide  solution,  and  4  c.c  of  concentrated  HCl.  In  the  presence 
of  fonnaldehyde  a  brilliant  fuchsin-like  colour  is  produced,  which 
reaches  its  full  intensity  after  a  few  minutes'  standing,  and  keeps 
without  marked  deterioration  for  several  hours. 

The  addition  of  ferricyanide  oxidizes  the  formaldehyde  condensa- 
tion product  to  a  substance  which  is  a  weak  base,  which  forms  a 
scarlet  hydrochloride.  This,  on  dilution,  undergoes  hydrolytic 
dissociation,  yielding  a  base  which  can  be  extracted  with  ether  to 
form  a  yellow  solution.  If  this  latter  be  shaken  with  concentrated 
HCl,  the  base  passes  back  into  aqueous  solution  in  the  form  of  the 
scarlet  hydrochloride.  This  reaction  detects  formalin  in  concentra- 
tion of  I  part  in  1,000,000.  It  is  quantitatively  best  applied  when 
the  concentration  is  i  in  50,000. 

From  two  standard  solutions  containing  respectively  i  in  10,000 
and  I  in  100,000,  it  is  possible  to  make  a  series  of  dilutions  from 
I  part  in  1,000,000  upwards  to  serve  as  a  colour  scale  when  the 
reaction  is  quantitatively  applied. 

Methylene-imino  derivatives  can  be  readily  hydrolysed  by  cold 
water;  with  ammonia,  formaldehyde  forms  a  somewhat  more  stable 
derivative;  and  with  Witte's  peptone,  under  certain  conditions,  an 
insoluble  product  from  which  formaldehyde  is  only  eliminated  with 
some  difficulty. 

By  modification  of  the  above  reaction  formaldehyde  can  be  de- 
tected in  all  such  combinations.  If  the  mixture  containing  such 
product  be  warmed  after  addition  of  phenylhydrazine,  the  aldehyde 
after  scission  combines  immediately  with  phenylhydrazine  to  form 
a  stable  condensation  product.  This  reaction,  being  irreversible, 
proceeds  to  completion.  On  the.addilion  of  the  ferricyanide  and 
HCl,  the  colour  is  developed  in  its  full  brilliancy. 

In  the  same  manner,  by  heating  after  addition  of  phenylhydrazine, 
formaldehyde  can  be  detected  when  present  in  its  polymerized  form. 

Heat  10  grammes  of  meat  (minced)  with  distilled  water  on  a 
boiling-water  bath  for  five  minutes.  Where  the  concentration  is 
I  part  formaldehyde  in  50,000  or  less,  10  c.c.  of  water  is  sufficient. 
Where  the  concentrations  are  higher,  larger  quantities  of  water  must 
be  employed.  To  every  10  c.c.  of  water  used  add  2  c.c.  of  a  i  per 
cent,  phenylhydrazine  h^^drochloride  solution.     Cool  and  filter  from. 


3i8  PRACTICAL  SANITARY  SCIENCE 

the  coagulum  through  cotton-wool.  To  12  c.c.  of  the  filtrate  add 
I  c.c  5  per  cent,  potassium  ferricyanide  and  4  c.c.  concentrated  HCl. 
Compare  colour  with  standards  made  from  the  standard  formalde- 
hyde solutions. 

It  has  been  found  that  in  chilled  beef  treated  by  formaldehyde 
the  superficial  fat  contains  distinct  quantities  of  formaldehyde; 
muscular  tissue  unprotected  by  fat  is  more  largely  contaminated 
than  other  parts. 

Grilling  of  meat  but  slightly  diminishes  the  amount  of  formalde- 
hyde, and  apparently  causes  the  aldehyde  to  penetrate  farther  into 
the  interior.  Boiling  greatly  diminishes  it.  Roasting  gets  rid  of 
most  of  it.  Sausages  made  from  meat  impregnated  with  formalde- 
hyde and  cooked  in  the  ordinary  way,  retain  it.  A  common  depth 
of  penetration  into  muscular  tissue  is  20  millimetres. 


Arsenic  in  Foods. — See  Reports  of  the  Royal  Commission  on 
Arsenical  Poisoning,  1903.  Cd.  1869.  Minutes  of  Evidence  and 
Appendices,  Vol.  II.,  especially  Appendices  16,  p.  183;  19,  p.  201; 
20,  p.  206;  21,  p.  208;  22,  p.  220;  24,  p.  230. 


Estimation  of  Araehis  Oil  found  as  an  Adulterant  in  Olive 

Oil. — Saponify  5  grammes  of  the  sample  with  25  c.c.  alcoholic 
potash  solution  (8-5  per  cent.).  Add  that  quantity  of  acetic  acid 
which  has  previously  been  found  by  titration  to  exactty  neutralize 
25  c.c.  of  the  above  alcoholic  potash,  and  cool  the  vessel  in  w-ater. 
Let  stand  for  two  hours.  Filter  off  the  acids  on  a  filter-paper, 
and  wash  them  with  70  per  cent,  alcohol  containing  i  per  cent.  HCl. 
Dissolve  the  acids  on  the  filter  with  about  40  c.c.  boiling  alcohol 
(95  per  cent.).  Add  about  10  c.c.  of  water  to  bring  down  the  alcohol 
to  about  20  per  cent.,  and  cool  down  to  room  temperature.  Filter 
after  an  hour,  and  wash  the  precipitate  with  70  per  cent,  alcohol. 
Dry  the  precipitate  (arachidic  acid)  at  100°,  and  weigh.  As  ara- 
chidic  acid  forms  about  5  per  cent,  of  araehis  oil,  the  weight  of  the 
oil  is  readily  calculated. 

Bakingr-Powders. — These  preparations  consist  of  an  acid  and 
an  alkaline  constituent,  and  a  third  inert  body — generally  starch — 
intended  to  absorb  moisture,  and  thereby  prevent  premature 
chemical  action.  The  alkaline  constituent  is  almost  always  bi- 
carbonate of  soda.  The  acid  constituent  may  be  (i)  tartaric  acid  or 
an  alkaline  bitartrate ;  (2)  acid  phosphate  of  calcium;  or  (3)  an  alum. 

Whilst  sodium  bicarbonate  and  tartaric  acid  are  free  from  calcium 
sulphate,   acid   calcium   phosphate   (used   in   the  manufacture   of 


APPENDIX  319 

baking-powder  and  self-raising  flour)  always  contains  more  or  less 
of  this  contamination. 

Estimation  of  CaSO^. — {a)  Ca:  Dissolve  10  grammes  of  the 
sample  in  boihng  dilute  HCl;  add  slight  excess  of  ammonia,  then 
slight  excess  of  acetic  acid,  and  filter  off  any  precipitate  that 
may  form.  To  the  filtrate  add  excess  of  ammonium  oxalate :  collect 
the  precipitate  of  calcium  oxalate  on  a  filter;  wash;  dry  in  an  air 
oven;  ignite;  cool  and  weigh  as  CaO. 

{b)  Sulphate  as  SO3:  Dissolve  10  grammes  of  the  sample  in 
boihng  dilute  HCl  as  above;  add  sHght  excess  BaClg,  and  allow 
the  precipitate  of  BaS04  to  settle.  Filter;  wash  the  precipitate  free 
from  chloride;  dry  in  air  oven;  incinerate;  cool  and  weigh.  The 
weight  of  the  ash  minus  the  weight  of  the  ash  of  the  filter-paper  x 
0-3434  =  weight  of  sulphates  as  SO3  in  10  grammes. 

[BaS04  =  233;  SOg^So;  ^  =  0-3434]. 

Estimation  of  Available  CO^  in  Baking-Powder. — ^An  exact  method 
is  that  recommended  by  Fresenius  in  which  a  small  quantity  (say 
O'5-i  gramme)  of  the  powder  is  acted  upon  by  water,  and  the 
evolved  gas  absorbed  by  soda-Hme.  When  all  the  gas  that  will  come 
off  is  absorbed,  the  remainder  of  the  COg  can  be  evolved  by  dilute 
acid  and  estimated  in  the  same  manner;  or  a  fresh  sample  may  bs 
operated  on  by  acid,  giving  the  total  COg:  this  figure  minus  the 
available  CO2  gives  the  unavailable  or  residual  gas. 

Estimation  of  Tartaric  Acid. — Wash  5  grammes  of  the  powder 
into  a  500  c.c.  flask  with  100  c.c.  water.  Add  about  15  c.c.  con- 
centrated HCl,  and  dilute  with  water  up  to  the  mark.  When  starch 
and  other  insoluble  matters  have  settled  out,  filter  the  liquid.  To 
50  c.c.  of  the  filtrate,  corresponding  with  ^  gramme  of  the  powder, 
add  10  c.c.  of  a  30  per  cent,  solution  of  carbonate  of  potash,  and  boil 
for  half  an  hour.  Filter  and  wash  precipitate.  Evaporate  filtrate 
and  washings  to  about  10  c.c.  Add  4  c.c.  glacial  acetic  acid  whilst 
stirring  vigorously,  and  100  c.c.  95  per  cent,  alcohol,  and  continue 
the  stirring  till  the  precipitate  appears  crystalline.  Stand  until 
precipitate  separates  out  (several  hours  may  be  required) ;  decant 
the  liquid  through  a  small  filter ;  wash  the  precipitate  on  to  the  filter 
with  alcohol;  wash  out  the  dish  with  alcohol,  and  the  precipitate 
with  the  same,  till  free  from  acetic  acid.  Now  boil  precipitate,  and 
filter  with  water  in  a  beaker.  Finally,  titrate  the  liquid  with  deci- 
normal  alkah  (using  phenolphthalein  as  indicator)  to  obtain  the 
amount  of  tartaric  acid. 


Lead  and  Arsenic  in  Tartaric  Acid,  Citric  Acid,  and  Cream  of 
Tartar. — See  Local  Government  Board  Food  Reports,  No.  2,  1907. 


320 


PRACTICAL  SANITARY  SCIENCE 


Approximate  Atomic  Weigrhts 


Ag       ... 

10  8-0 

I 

12.7-0 

Al        .. 

27-0 

K 

39-0 

As        .. 

75-0 

Mg       . . 

24-0 

Ba        .  . 

137-0 

Mn       . . 

55-0 

Br 

80 -0 

N 

14-0 

C 

12-0 

Na        .  . 

23-0 

Ca         .. 

40-0 

0 

16-0 

CI         .. 

35-5 

P 

31-0 

Cr         .. 

•       52-0 

Pb        . . 

206-0 

Cu        .. 

63-0 

S 

32-0 

Fe        .. 

56-0 

Sn         .. 

119-0 

H 

i-o 

Zn        . . 

65-0 

A  litre  of  water  saturatetl  with  air  at  10°  C.  dissolves  8-68  c.c.  O 
at  N.T.P. 

A  litre  of  water  saturated  with  air  at  15°  C  dissolves  6-96  c.c.  O 
at  N.T.P. 

A  litre  of  water  saturated  \\ith  air  at  20°  C.  dissclves  6-28  c.c.  O 
at  N.T.P. 

One  hundred  grammes  of  water  at  15°  C.  will  dissolve  the  following 
amounts  expressed  in  grammes  of  the  salts  indicated: 


BaSOj   .. 

o-oob 

KBr       . . 

.     38-500 

CaS04    .. 

0-208 

CaClo     .  . 

.     40-800 

Ba(NO.O., 

7-800 

NH4Br  . . 

.     44-900 

NaHC6.j' 

8-800 

NaBr     .  . 

.     46-500 

K2SO,  ■. . 

9-600 

SrBr.,     . . 

.     50-300- 

Na.,SO, 

11-900 

Mg(N03), 

.     50-500 

KHCO., 

. .     18-300 

BaBr.,    .  . 

.     51-000. 

KNO3  ■  . . 

.  .     21-200 

Ca(NOo)., 

•     53-800 

NaaCbg 

. .     22-000 

NH4N63" 

•     55-300- 

KCl        . . 

. .     25-000 

KI 

.     58-500. 

NH4CI   .. 

. .     26-500 

Nal 

.     63-500 

(NH4),S04        . 

.  .     33-200 

Balo       .  . 

.     66-900 

MgSO^  . . 

.  .     34-000 

MgCl,    .. 

,     66-900 

NaNOg 

.  .     34-200 

Cal./     .. 

.     67-000 

NaCl      . . 

.  .     36-100 

KXO3    .. 

.    100-000' 

The  following  salts  contain  the  numbers  of  molecules  of  water 
of      crystalhzation      indicated:      BaCl.„2HoO;      Na„HP04,i2H,0 
Na.,S.,0„5HoO;     Pb(aH30.,)o,3H20;     ZnSOJ^H.^O;  "  FeS04.7H'0 
CuS04,5H.,d;      AlK(S04)o,i2HoO;      MgSOj^HoO;      H„C.,04,2H.;0 
Cu(NH4)„;6HoO;  CuCU,2(5:H4).,C1,2H.,0;  NaNH;HP04,4H,0  (micro- 
cosmic    "salt);      CaCr.,6HoO;"    Na.,S04,ioH20;     Na,B407,ioH20; 
(NH4)2(S04)2,6H20;  MgS04",K.S04,6"HoO. 


INDEX 


AcARUS  domesticus,  203 

farinas,  221 
Acetyl  value,  195 

Acid,  acetic,  224,  252,  253,  259,  260, 
264,  268 

benzoic,  178 

boracic,  174,  187 

carbolic,  301 

citric,  166,  267,  268,  317 

hypochlorous,  296 

lactic,  252,  253 

malic,  253,  259,  260 

oxalic,  134 

phosphoric,  268 

salicylic,  177,  223 

sulphuric,  224,  267,  268 

sulphurous,  254 

tannic,  257,  258,  259 

tartaric,  259,  267 

value  of  fat,  192, 
Acidity  of  beer,  253 

of  bread,  231 

of  milk,  155 

of  spirits,  264 

of  water,  15,  16,  95 

of  wine,  259,  260 
Actinomycosis,  233 
Adams's  process,  157 
Adeney's  process,  loi 
Adsorption,  292 

Adulteration    (see   preservatives)    of 
beer,  254 

of  bread,  231 

of  butter,  185,  187,  189 

of  cheese,  203,  205 

of  cocoa,  285 

of  coffee,  281 

of  milk,  172 

of  mustard,  269 

of  pepper,  270 

of  sugar,  274 

of  tea,  278 

of  wines,  259 
>;Ecidium  berberidis,  226 
Air,  118 

ammonia  in,  140,  144,  145 
ammonium  sulphide  in,  140,  141, 

144.  145 
bacteria  in,  146 


Air,  bromine  in,  141 

carbon  dioxide  in,  133,  134,  135, 
136 

carbon  disulphidc  in,  141 

carbon  monoxide  in,  136 

chlorine  in,  141 

composition  of,  118 

humidity  of,  129,  130 

noxious  gases  in,  144 

oxygen  in,  130 

ozone  in,  141 

sewer,  143 

sulphur  dioxide  in,  140 

sulphuretted  hydrogen  in,  140 

suspended  matter  in,  143 
Albuminoid   (organic)   ammonia,   41, 

42,  46,  47,  52,  81,  92 
Alcohols,  246,  251,  252,  259,  262 

amyl  alcohols,  247 

butyl  alcohols,  247 

diethyl  carbinol,  247 

estimation  of  alcohol,  252 

ethyl  alcohol,  247,  251,  252,  253 

isobutyl  carbinol,  247 

methyl  alcohol,  246,  247 
butyl  carbinol,  247 

propyl  alcohols,  247 

table,  265 
Alkaline  permanganate,  44 
Alluvium,  3 
Aloes,  254 
Alum,  231 

Ammonia-free  water,  42 
AmcEba,  69,  70,  75 
Anabasna,  10,  72 
Anguillulae,  70,  237 
Animal  parasites,  236 

spine,  71 
Ankylostomum  duodenale,  116 
Annatto,  179,  199 
Antipyrin,  288 
Antiseptic,  287 
Apjohn's  formula,  129 
Arrowroot,  220,  221 
Arsenic,  254,  317 

estimation  of,  255,  256 
in  foods,  316 
Ascarus  lumbricoides,  237,  242 
Ascocarps,  228 


321 


3-2^ 


PRACTICAL  SAXITARY  SCIENCE 


Ascosporcs,  2  28 

Aspergillus  glaucus,  203,  222,  223 
Atomic  weights,  320 
Azotobacter,  114 

Babcock  method.  162 
Bacillus  botulinus,  245 

butyricus,  112 

toli  communis,  84,  85,  86,  87,  88, 
91.  104,  112,  117,  146,  181, 
245.  2S9,  293 

denitrilicans,  112 

enteritidis  sporogenes.  84,  85,  87, 
88,  117,  146,  iSi,  245 

fluorescens,  200 

fluorescens  liquefaciens,  112 

Johnc,  182 

Klebs-Loffler,  182 

lactis  aerogenes,  112 

mallei.  234 

mesentericus  vulgatus,  112 

mist  bazillus.  182 

Holler's.  181 

mycoides,  112 

oedematis  maligni,  116 

paratN-phosus  B.  245 

prodigiosus  (micrococcus),  5,  89 

proteus  vulgaris.  112.  245 

proteus  zenkeri.  112 

putrificus.  112 
.   pj'ocyaneus.  89 

Rabinowitch.  1S2 

radicola,  113 

smegma,  1S2 

subtilis,  112 

suipestifer,  245 

tetani,  116 

tuberculosis,  84,  181,  182.  200, 
205,  233,  253 

t\-phosus,  I,  84,  85.  89,  116.  182, 
"  2S9,  293 
Bacteria  in  air.  146 

in  butter.  200 

in  meat,  233,  245 

in  milk,  180 
Bacterial  food-poisoning.  245 
Bacteriological  examination  of  water, 

2,  6 
Bacteriology  of  water,  83 
Bagshot  sands,  3 
Baking-powders,  318 
Barley,  209,  215,  216 
Barometers,  120,  122 

corrections  of,  122 

Fortin.  120 

Hooke's.  122 

Kew,  122 


Baudouin's  test,  199 
Bean,  2ir,  219.  221 
Bcch  's  test,  199 
Beer,  250 

acidity  of,  253 

alcohol  in,  252 

aloes  in.  254 

arsenic  in,  254 

bitters  in.  253 

boric  acid  in.  254 

gentian  in,  254 

malt  extract  in,  253 

salic\dic  acid  in.  254 

sodium  chloride  in.  254 

sulphurous  acitl  in.  254 
Beggiatoa  alba,  10,  71,  73,  74 
Beri-beri,  214 
Bicarbonates.  21.  66 
Birotation  ratio,  167 
Bismark  brown.  53 
Bitters,  253 
Bleaching  of  flour,  212 

powder,  296 
Boric  acid,  244.  254 
Boulder  clay,  3 
Boyle's  law,  119 
Brandy,  261,  262 
Bread,  229 

acidity  of.  231 

adulteration  of.  231 

alum  in.  231 

ash  of,  230 

composition  of,  229 

silica  in,  230 
Bromine.  298 

Brownian  movement,  305.  306 
Bruchus  pisi.  221 
Brucine  test.  54 
Bursaria  gastris,  10,  73 
Butter.  184 

adulteration  of.  185 

bacillus,  182 

bacteria  in,  200 

colouring  matters  in,  199 

composition  of,  184 

cottonseed  oil  in,  199 

curd  in,  187 

fat.  187.  189 

acetyl  value  of,  195 
acid  value  of,  192 
Hehner  value  of,  193 
iodine  value  of,  193 
melting-point  of,  190,  194 
microscopic  examination  of, 

192 
physical  properties  of.  190 
polarized  light  test,  198 


INDEX 


323 


Butter  i'at,  Polcnske  number,  197 
preparation  of,  189 
refractive  index,  192 
Reichert-Meissl  value,    195, 

203 
saponification  value,  192 
solidiiication-point,  191 
specific  gravity,  190 
titre  test,  191 
Valenta's  test,  198,  203 
Wijs's  test,  194 

preservatives  in,  187 
boric  acid,  187 
formalin,  187 
nitrates,  187 
salicylates,  187,  188 
sulphites,  187,  189 

saffron  in,  200 

salt  in,  187 

sesame  oil  in,  199 

starters  in,  200 

turmeric  in,  200 

water  in,  185 

Caelosphaerium,  10,  72 
Caffein,  282,  284 
Calandra  granaria,  222 
Calcium,  28 

saccharate,  184 
sulphate,  319 
Cane-sugar,  184,  207,  271 
Carbon  (organic),  39 
Carbon   dioxide  in    baking-powders, 
319 
in  beer,  251 
in  water,  65 
Carbonates,  21 
Carchassium  Lachmanni,  73 
Casein,  150 
Catchment  area,  2 
Catechu,  280 
Cellulose,  208 
Cereals,  209 
Chalk,  3,  4,  31,  80,  92 
Chamberland  bougie,  235 
Champagne,  258 
Chara  fragilis,  10,  70 
Charles's  law,  119 
Cheese,  201 

adulteration  of,  203 
ash,  203 
Brie,  202 
Camembert,  202 
Cheddar,  201,  202 
composition  of,  202 
fat  in,  203 
foreign  fat  in,  205 


Cheese,  Gorgonzola,  201 
Gruyerc,  201 
lactose  in,  205 
moulds  in,  203 
proteins  in,  204 
starch  in,  206 
Stilton,  201,  202 
Stracchino,  202 
tubercle  bacillus  in,  205 
Tyrothrix  in,  203 
water  in,  203 
water-soluble  N,  204 
Chemical  analysis  of  water,  2,  12 

balance,  12 
Chicory,  283 
Chinese  silk,  76 
Chloride  of  lime,  296 
Chlorides  in  water,  16,  18,  19,  20,  30 

59,  82 
Chlorine,  290,  295,  296,  297,  298 

in  air,  141 
Chocolate,  286 
Chromium,  36 
Claret,  257,  258 
Clark's  process,  25 

scale,  25 
Claviceps  purpurea,  227 
Clostridium  pastorianum,  ii4_ 
Coal,  3  '■"^ 

Coal-tar,  301 
Coccidia,  239 
Cocoa,  285 

composition  of,  285 
Coenurus  cerebralis,  236 
Coffee,  281 

composition  of,  281 
Colloidal  meixury,  293 
silver,  293 
solutions,  304 
Colour  of  water,  8 
Colostrum,  166 
Condensed  milks,  183 
Conferva  bombycina,  73 
Continuous  phase,  304 
Copper,  32 

sulphate,  3^,  313 
Copper-zinc  couple,  55 
Cosmarium,  70 
Cotton  fibres,  69,  72,  78 
Cream,  163 

of  tartar.  319 
Crenothrix,  8,  10,  71,  73 
Creolins,  289 
Cresols,  301,  308 
Crum's  method,  55 
Crj-^tomonas,  10,  70 
Crystalline  rocks,  3 


324 


PRACTICAL  SAXITARY  SCIENCE 


Cuprous    chloride    methocl    of    esti- 

.  mating  COo,  140 
Cysticcrcus  bovis.  23G 
ccUulosae,  236,  240 
tenuicoUis,  236 

Daphnia  pulcx,  71,  74 
Dangerous  water.  11 
Decinormal  solutions,  12 
Demodex  phylloidcs  suis,  236 
Deodorant,  287 
Dew-point,  128,  129 
Diamido-benzol,  53 
Diastase,  152,  208,  250 
Diatoms.  69,  70,  71,  72 
Dinitrodiphenylaminesulphoxide,  314 
Diphen\lamine  test,  54 
Disinfectants,  287 
Disperse  phase,  305 
Distoma  hcpaticum,  236,  241 

lanceolatum,  236 
Dotted  vessels  (chicory),  284 
Drepanido  taenia  lanceolata,  236 

Echinococcus  multilocularis,  238 
unilocularis,  238 

Egg  (Ascarus  lumbricoides),  69 
(Taenia  solium),  69 
(Trichocephalus  dispar),  69 

Elder-leaf,  278 

Emulsions,  305,  306 

Endorina,  72 

Entire  flour,  214 

Erosive  water,  16 

Esters  in  spirits,  264 

Ethers  in  wines,  260 

Euplotes  charon,  69 

Eustrongylus,  237 

Fat  (butter),  189 

(milk),  152,  153,  157 
Fault,  4 
Fehling's  method,  170 

Pavj'  modification,  171 
Filaria,  237 
Filtrable  viruses,  234 
Flax,  77 
Flock,  313 

Flour-improvers,  212,  213 
Formalin,    175,    188,   244,    290,    299, 

300,  316 
Frankland's  method,  39 
Free  and  saline  ammonia,  41,  42,  46, 

47,  52,  8r,  92 
Friedlander's  bacillus,  89 
Fungi,  68 
Furfural,  265 
Fusel  oil,  262 


Gases  in  water,  60 
Gentian.  254 
Geology,  3 
Gin,  264 

Glaisher's  formula,  129 
Glenodinium,  10 
Glucose,  271.  273 
Gluten,  210 
Gorgonzola  cheese,  201 
Graham  flour,  213 
Greensands,  3,  4 
Griess's  method,  53,  55,  57 
Ground  water,  5 
curve,  5 
Gruyere  cheese,  201,  202 

Haematosporidia,  239 

Hair  of  insect,  70 

Haldanc's  apparatus   for  estimating 

CO.,  315 

method  for  estimating  CO,  137 

Hardness  in  water,  20,  22,  25 

permanent,  24,  25,  26,  81 
temporary',  24,  25,  26 
total,  24,  26,  81,  92 

Hemp  fibre,  69.  77 

Hempel's  gas  burette,  131 

Hermite  solution,  296 

Hock,  258 

Houzeau's  test,  142 

Human  milk,  149,  153,  154 

Humulus  lupulus,  251 

Humus,  109,  no.  III 

Hydra,  69 

Hydrochloric  acid  in  air,  141,  144 

Hydrodictyon,  73 

Hydrogen  peroxide  in  air,  142 

as  disinfectant,  294,  295 
in  milk,  178 

Igneous  rocks,  5 

Infant's  foods,  205 

Infusoria,  69,  70 

Interpretation   of   chemical   analysis 

of  water,  79 
Iodoform  test,  251 
Ions,  297 

Iron  in  water,  2,  34,  82 
Ironstones,  3 
Isochlors,  17 

Jute,  78 

Kephir,  183 

Kimmeridge  cla^^  3 

Kjeldahl's  method,  98,  1G5,  184,  314, 

Koumis,  183 


INDEX 


32 


Lactalbumin,  151 
Lacteal  vessels,  284 
Lactic  acid,  155,  253 
Lactoglobulin,  151 
Lactose,  149,  152,  167,  205,  207 
Laplace's  formula,  124 
Lard,  205 

Lead  in  spirits,  262,  317 
in  water,  30,  32,  82 
Leffmann-Beam  process,  162 
Lemon-juice,  267 
Leptomitus  lacteus,  73 
Lias,  3 

Lime-juice,  267 
Limestone,  3 
Linen,  69 

Lolium  temulentum,  229 
London  clay,  3 

Lunge  and   Zeckendorf's   estimation 
of  carbon  dioxide,  135 

Magnesium  in  water,  28 
Maize,  209,  217 
Malt  extract,  253 
Manganous  chloride,  64 
Marquardt  method,  261 
Marsh's  test,  255 
Maximum  thermometer,  126 
Meat,  253 

inspection,  233 

parasites  (animal)  in,  236 

preservatives  in,  244,  316 

tuberculosis  in,  233 
Melosira,  71 
Meridion,  10 

Metallic  impurities  in  water,  261 
Metaphenylene-diamine,  53,  56 
Methyl  alcohol,  263 
Methyl  butyl  carbinol,  247 
Methylene- imino     compounds,     244, 

316 
Methyl  orange,  25 
Milk,  149 

acidity  of,  155 

Adams's  process,  157 

adulteration  of,  172 

analysis  of,  155 

annatto  in,  179 

ash,  164 

bacteria  in,  181,  182 

benzoic  acid,  178 

boracic  acid,  174 

casein,  150 

cellular  elements  of,  183 

citric  acid,  166 

colostrum,  166 

colouring  matters,  179 


Milk,  comi)ositif;n  of,  149 
human,  153 

condensed,  183 

cream,  163,  184 

calcium  saccharate  in,  iHj 
cane-sugar  in,  184 
gelatin  in,  184 
starch  in,  184 

dried,  183 

fat,  152, '153.  157 

formalin,  175 

heated,  167 

human,  153 

hydrogen  peroxide,  178 

lactalbumin,  151 

lactic  acid,  155 

lactoglobulin,  151 

lactose,  152,  167,  180 

muco-protein,  151 

mystin,  178 

pasteurized,  167 

reaction  of,  155 

Rose-Gottlieb  method,  163 

salicylic  acid,  177 

sodium  carbonate,  178 

solids  not  fat,  165 

sour,  179 

specific  gravity,  155 

streptococci  in,  182 

total  solids,  163 

turmeric,  179 

Werner-Schmidt  method,  160 

Westphal  balance,  157 
Millet,  209 

Miniraum  thermometer,  126 
Moniezia  expansa,  236 
Moulds,  203 

Mucor  mucedo,  203,  222 
Mucilage  cells,  269 
Mustard,  269 
Mustard  oil,  269 
Mycoderma  aceti,  268 
Myxosporidia,  239 

Navicula,  72 

Nessler's  reagent,  42,  57 

New  red  sandstone,  3 

Nitrates  in  water,  51,  52,  53,  54,  57, 

82 
Nitric  acid  in  air,  141 

organisms,  39 
Nitrites  in  water,  51,  52,  53,  82 
Nitrobacter,  112 
Nitrogen  as  amides,  204 

as  ammonia,  205 

as  caseoses,  204 

(organic),  39 


326 


PRACTICAL  SANITARY  SCIENCE 


"Nitrosomonas  Europita,  112 
Nitrous  acid  in  air,  141 

organisms,  39 
Nonnal  solution,  12 
Nostoc,  71 

Oat,  209,  217 
Odour  of  water,  8 
(Enocyanin,  257 
Qistrus  bovis,  23(3 
Old  red  sandstone,  3 
Oolite,  3 

Ordnance  survey,  3 
Organic  carbon,  39 

matter  in  air,  315 
in  water,  38 

nitrogen,  39 
Oscillatoria,  72 
Oxidizablc  organic  matter,  47 
Oxidized  nitrogen,  51 
Oxygen  absorbetl  from  permanganate, 
47.  50,  90,  91,  92,  93.  94.  95. 
96,  97.  99 

dissolved  in  water,    Go,   63,    99, 
100 
Oxyuris  vermicularis,  237,  243 
Ozone,  295 

Pandorina,  72 
Paraform,  300 
Paramoecium,  69,  71 
Parasites  in  meat,  236 
Pasteurized  milk,  167 
Pavy-Fehling  method,  171 

solution,  275 
Pea,  219 
Peat,  5 

Penicillium  glaucum,  203,  222 
Pentastomum  taenioides,  239 
Pepper,  269 
Peronospora,  222 
Pettenkofer's  method,  133 
Phenol,  289,  292,  302 
Phenolphthalein,  15,  65,  66 
Phenolsulphonic  acid,  57 
Phenylhydrazine  hydrochloride,  317 
Phenyloids,  303,  304,  306,  307 
Phosphates  in  water,  27,  28,  30,  82 
Phosphoretted  hydrogen,  142 
Phosphorus  compounds,  232 
Physical  examination  of  water,  7 
Picric  acid,  57 
Piophila  casei,  203 
Plastering  of  wine,  259 
Pleurococcus,  70 
Plumbo-solvency,  16,  27,  95 
Poisonous  metals  in  water,  30 


Polarimetry,  lOS 

I'olishetl  rice,  214 

Porosity  of  soil,  106 

Port  wine,  258 

Post-tertiary  deposits,  3 

Potassium  sulphate  in  wine,  260 

permanganate,  298 
Potato,  220 

Pouchct's  aeroscope,  143 
Primary  deposits,  3 
Proteus  vulgaris,  89 
I'uccinia  graminis,  225 
Purbcck  marble,  3 
Putrefaction,  39 

Qualitative  examination  of  air,  144 
Ouassia,  254 

Rain,  6 

Reaction  of  water,  13,  91,  92,  93 

Reinsch's  test,  256 

l^clative  humidity,  130 

Resin  acids,  307 

Rice,  209 

I^ideal- Walker  coefticient,  312 

method,  304,  307 
Rivularia,  10 
Rose's  method,  263 
Rum,  264 
Rye,  209 

Saccharomyces  ellipsoideus,  257 

Salicylic  acid,  224 

Sarcosporidia,  239 

Sea-water,  95 

Self-registering  thermometer,  125 

Sesame  oil,  199 

Sewage,  i,  2,  81,  92,  94,  96 

effluents,  60 

fungus,  9 
Shales,  3 
Shallow  wells,  3 
Sherry,  258 
Silica,  29,  230 
Silk,  76 

Six's  thermometer,  125 
Sloe-leaf,  278 
Soaps,  20,  21 
Sodium  chloride  in  beer,  254 

tetrathionate,  49,  60,  62 

thiosulphate,  49,  60,  63 
Soil,  105 

bacteria  in,  iii 

clay,  107 

humus,  109 

lime,  108 

magnesia,  108 


INDEX 


327 


Soil,  organic  matter,  107 

pcrniLeability  of,  107 

porosity  of,  106 

sand,  107 

specific  gravity  of,  106 
heat  of,  106 
Soxhlet's  apparatus,  159 
Sphserotilus  natans,  71 
Spirits,  261 
Spirogeira,  71 
Sporsndonema  casei,  203 
Sprengel's  method,  57 
Standard  ammonium  chloride,  42 

arsenical  mirrors,  255 

arsenious  acid,  297 

bromate  bromide,  302 

calcium  chloride,  22 

copper,  33 

iron  alum,  35 

lead,  31 

nitrate,  57 

nitrite,  54 

iodide,  62 

oxalic  acid,  134,  298 

permanganate,  48,  49 

silver,  18 

soap,  22,  23 

solutions,  12,  14 

thiosulphate,  296 

zinc,  37 
Staphylococcus  pyogenes  aureus,  298, 

303 
Starch  granules,  211 

arrowroot,  220 

barley,  215 

bean,  219 

maize,  217 

oat,  217 

pea,  219 

potato,  220 

lice,  216 

rye,  215 

sago,  218 

tapioca,  218 

wheat,  215 
solution,  48 
Starters,  200 
Stokes's  tube,  161 
Straight  run  flour,  214 
Streptococci,  86,  112,  182 
Strongylus,  237 
Substrate,  249 
Sugar,  260,  270 

Sulphate  of  calcium  in  tea,  278 
Sulphates  in  water,  29,  30,  82 
Sulphur  dioxide,  144,  145,  297 
Sulphurous  acid,  254 


Suspicious  water,  1 1 
Synedra,  70 
Synura  uvella,  72 

Tabaric's  method,  253 
Tabellaria,  10 
Taenia  cocnurus,  236 

echinococcus,  236,  238 

marginata,  236 

saginata,  237,  241 

serrata,  236 

solium,  237,  240 
Tartaric  acid,  260,  267,  319 
Taste  (water),  10 
Tea,  275 

adulteration  of,  2 78 

composition  of,  277 

leaf,  276 

tannin  in,  280 

thein  in,  277,  278,  279 
Teleutospores,  226 
Tertiary  deposits,  3 
Testa  cells  (coffee),  283 
Theobi'omine,  286 
Thermometer,  125 
Thiosinamine,  269 
Thresh's  method,  60 
Thymol,  291 
Tidy's  method,  47 
Tilletia  caries,  224 
Tin,  33,  313 
Titre  test,  191 
Tobacco-leaf,  279 
Triamidoazobenzol,  53 
Trichina  spiralis,  237 
Trichocephalus,  237 
Trinitrophenol,  57 
Turbidity  (water),  7 
Turmeric,  179,  199,  200,  269 
Two-foot  tube,  8 
Tylenchus  tritici,  222 
Tyrothrix,  203 

Ulothrix,  70 

Ultramicroscopic  viruses,  235 
Upland  surface  waters,  50,  52 
Uredo  foetida,  224 
Uroglena,  10,  70 
Ustilago  segetum,  223 

Vapour  tension  table,  127 

Vernier,  121 

Vibrio  cholerse  asiatics,  i 
tritici,  221 

Vinegar,  268 

acetic  acid  in,  268 
mineral  acid  in,  268 


328 


PRACTICAL  SANITARY  SCIENCE 


Vinegar,  nitrogen  in,  268 

phosphoric  acid  in,  268 

specific  gravity  of,  268 

sulphuric  acid  in,  268 

total  solids  of,  269 
Viscosity,  304 
Volvox,  72 
Vorticella,  71,  72,  75 

Water,  i 

acidity  of,  15,  i(),  95 
albuminoid  ammonia  in,  41.  42, 

4O,  47,  52,  81,  92 
algae  in,  68,  69,  70,  71,  72,  73,  79 
alumina  in,  21 
anabaena  in,  10,  72 
Bacillus  coli  in,  84,  85,  80,  87,  88, 

91 
bacteriological  examination  of,  83 
bear,  73 

biological  examination  of,  2,  G7 
calcium  in,  28 
carbon  dioxide  in,  65,  66 
chalk  in,  27,  80 

chemical  examination  of,  2,  12 
chlorides  in,   16,   18,   19,  20,  30, 

59.  8^ 
chromium  in,  36 
colour  of,  8 
copper  in,  32 
crystallization  of,  317 
cycle,  6 
dangerous,  11 
enzymes  in,  ^S 
erosive  action  of,  i(j 
free  and  saline  ammonia  in,  41, 

42,  46,  47,  52,  81,  92 
hardness  of,  20,  22,  24,  25,  26, 

81,  92 
iron  in,  2,  34,  82 
lead  in,  30,  32,  82 
magnesium  in,  28 
nitrates  in,  51,  52,  53,  54,  ^j,  82 
nitrites  in,  51,  52,  53,  82 
odour  of,  8 
organic  matter  in,  38 
oxidizable  organic  matter  in,  47 
oxygen  dissolved  in,  60 
peaty,  5 

phosphates  in,  27,  28,  30,  82 
physical  examination  of,  2,  7,  91, 

92,  93.  94.  95 
plumbo-solvency  of,  16,  27,  95 
poisonous  metals  in,  30 
pure,  91 


Water,  rain,  6 

reaction  of,  13,  91,  92,  93 

sediment,  67 

silica  in,  29 

solitl  residue  of,  27,  92 

sulphates  in,  29,  30,  82 

suspicious,  II 

taste  of,  10 

tin  in,  33 

total  solids  in,  92 

turbidity  of,  7 

wholesome,  11 

zinc  in,  36,  Sz 
Weald  clay,  3 

Werner-Schmidt  method,  160,  203 
Westphal  balance,  157 
Wheat,  209 

flour,  209 

ash  of,  211 
composition  of,  210 
fat  of,  210 
gluten  of,  210 
starch  granules  of,  211 
sugar  of,  210 
water  of,  211 
Whisky,  261 

acidity  of,  264 

alcohol  of,  262 

furfural  in,  265 

fusel  oil  in,  262 

metallic  impurities  in,  262 

methyl  alcohol  in,  263 
Wholemeal  flour,  213 
Willow-leaf,  278 
Wine,  256 

acidity  of,  259 

alcohol  of,  259 

ash  of,  260 

colouring  matter  in,  259 

ethers  of,  260 

extract  of,  260 

plastering  of,  259 

potassium  sulphate  in,  260 

sugars  in,  260 

water  in,  259 
Winkler's  method,  63 
Witte's  peptone,  308 
Wood  cells,  69,  72 
Wool,  69,  70,  76 

Xylenols,  303 

Zinc  in  water,  36,  82 
Zymase,  249 
Zj^molyte,  249 


Baillicre,  Tintlall  <5t^  Cox,  3  Henrietta  Street,  Ccrvent  Garden 


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